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PeeCTRIC LIGHTING 


A 


PRACTICAL EXPOSITION OF THE ART 
FOR THE USE OF 
ENGINEERS, STUDENTS, AND OTHERS INTERESTED IN 


THE INSTALLATION OR OPERATION OF 
ELECTRICAL SECANTS 


VOLUME II. 


DISTRIBUTING SYSTEM AND LAMPS 


BY 


Pia Nl be CROC KOR JE i Pay: 


PROFESSOR OF ELECTRICAL ENGINEERING IN COLUMBIA UNIVERSITY, NEW YORK. 
PAST—PRESIDENT OF THE AMERICAN INSTITUTE 
OF ELECTRICAL ENGINEERS 


FR He Di Ga] Oe. 





NEW YORK , 
D. VAN NOSTRAND COMPANY 


LONDON 


Pec te NE SPON «LINER: 
57 HAYMARKET, S. W. 


1904 . 


Copy RIGHT, 1961, 


By D. Van NostTrRAnpD ComMPany. 


eM kal Si nw Od wh 


In presenting this second volume on the subject ‘of Electric 
Lighting, attention is called to the fact that it relates to the 
conductors for transmitting and distributing the current, commonly 
called the distribution system, to the lamps, the supply of which is 
the final object of the entire system, and to the various auxiliary 
devices, such.as switches, cut-outs, meters, etc., employed in con- 
nection with the same. In short, the present volume covers all 
parts of electric lighting systems outside of the generating plants, 
the first volume being devoted to the latter. The properties of 
conductors and various systems of electrical distribution, including 
direct current, as well as single and polyphase currents, occupy 
the first half of the book. Overhead and underground conductors 
are next discussed, and then arc lamps are treated: in considerable 
detail, since they are important features in electric lighting, and 
have not been very fully treated in other publications. Interior 
wiring, incandescent and other forms of lamps, and finally electric 
meters are given considerable attention. An appendix, containing 
the National Electrical Code, and another the Report of the Com- 
mittee on Standardization are included, these being the rules which 
must, or at least should be, followed in constructing or operating 
any electrical system. In treating each branch of the subject, the 
principles have first been given with considerable fullness, being 
followed by practical examples of the prominent methods and 
forms of apparatus employed in actual practice. In the space 
available it has been impossible to go deeply into any subject, but 
the attempt has been made to cover the important elements and 
their relation, so that they may be understood and used success- 
POLL Veer | 

Both volumes are intended as text books for engineering 
schools and as hand books for practicing engineers, and for that 


800242 


1V PREFACE. 


reason abstruse and detailed matter has been omitted as far as 
possible. 

The National Electrical Code, containing the requirements ac- 
cording to which all electric lighting and other installations should 
be made, is so important that itis printed in full in Appendix I. 
The corrections made in December, 1900, were anticipated, and 
have been incorporated. The Report of the Committee on Stand- 
ardization of the American Institute of Electrical Engineers being 
also of fundamental importance, is given in full in Appendix II. 

The author is glad to take this opportunity to thank many 
friends for information and assistance. Messrs. J. W. Lieb, C. W. 
Rice, and P. Torchio of New York, and Mr. W. S. Barstow of 
Brooklyn, kindly gave the benefit of their wide experience in con- 
nection with electrical distribution. Messrs. Clark and McMullen of 
New York rendered valuable assistance in connection with overhead 
and underground conductors. To Mr. Joseph Bijur the author is 
specially indebted for a great deal contained in the chapters on the 
electric arc and arc lamps. - Mr. John W. Howell, of the General 
Electric Lamp Works, very kindly read over the proof of the 
chapter on incandescent lamps, in which subject no one has had 
greater and more successful experience. Mr. C. S. Aylmer-Smail 
assisted the author in collecting material, in proof-reading, and in 
other ways. Finally, thanks are due to the General Electric, 
Westinghouse, and other companies, which have freely given 
information and illustrations. 


(ORIN EE INR LDS: 





CHAPTERS 1. PAGE 


ELECTRICAL DISTRIBUTION, PHYSICAL PROPERTIES OF CONDUCTORS , . j 


CHAPTER II. : 


SHRIPNSEOVSEEMSEON sie RGrRIGA TWD TS DRIP UWL TONG se cea 6 allen oe i 


CHAPTER Til. 


RARAR EMD OVSLEMS OFLU bCERICALIOISDRIBUTIONG sii. ela con cae) 2 28 


CHAPTER IV. 


THREE— AND FIVE-WIRE SYSTEMS OF DISTRIBUTION . . . : 2. » © . 70 
CHAPTER Va 
DIRECT CURRENT TRANSFORMER SYSTEMS OF ELECTRICAL DISTRIBUTION . 93 


CHAPTER VI. 


NET WOR KSVORNILLECT RICAL? CONDUCTORS. 4) Bsc ts + Shad cova. ten el, oh enk s LOS 
CHAPTER VII. 


PRINCES OLE AL TERNATINGECMRRENTS tk.) otek so. a ep a8 a) a) ee LOS 


CHAPTER VIIL- 


RRINCEEME STORE AE TL DRNA TING EOLYPHASE, (GURRENTSH 6. <6 ene cose) 4 


CHAPTER IX. 
Porshe Eh Smee ey en ee Pn lan SPM) Gabe el oh “olf on ae AAD 


CHAPTER X. 


ATrTorwvarTine: CURRENT OYSTEMS OF. DISTRIBUTION 4 9/7. 6 6: * ‘s «6 18 


CHAPTER: 


CALCULATION OF ATLERNATFING CURRENT CIRCUITS 2)... 6 eh oe » of 224 
CHAPTER XII. 
UE CAGMELECERICAL CONDUCTORS .. . 2 «on ee ee dee) se (ees oOL 


CHAPTER XIII. 


UNDERCROUNITeHTROTRICAT, CONDUCTORS 9. 2. eu 0s 20 we 60 ae cw ss 208 


V1 CONTENTS. 
CHAPTER XIV. ie PAGE 


Tuk /EVyECTRIC ARC <s0i.Piaceee Fe eek wc es ee 


CHAPTER XV. 
ARC LAMPS, e . e e e e . e e ° ° . . e e e ® e ° bd ® e° o 329 


CHAPTER’ XVI. 
INTERIOR WIRING © 46% eames le is @:s0_ << Stoke ae ode Meme lie [ete ous 6's elle mine 371 


CHAPTER XVII. 
INCANDESCENT) GAMPS:.. 50 PERS egies wale tae ea cin ne ieee 


CHAPTER XVIII. 
LAMPS ‘NOT EMPLOYING /CARBON MS a0 bee, acs es ne ie ce) gcse aug Sie eee oa 


CHAPTER XIX. 
ELECTRIC METERS’ WC St. SO eee ae OR, whe eee ce ls) egies eee 


APPENDIX I. 
NATIONAT, “ELECTRIC GODE. #25 ee niet src s -1 0s tie tice bc a ole otc Rca een Erk 


APPENDIX II. 
REPORT OF THE COMMITTEE ON STANDARDIZATION: .° 5 «© ce ce © ce © « 400 


INDEX ° ° e © ° e ® ° e ° ° ° ° ° e e ° e ® e ® ® e ° « 503 


ELECTRIC LIGHTING. 


OMIT TER AE 
ELECTRICAL DISTRIBUTION. 


PHYSICAL PROPERTIES OF CONDUCTORS.. 


THE distribution of electrical energy from the generating plant 
to lamps, motors, or other devices, involves problems of great sci- 
entific and technical interest. It is also a fact that in almost every © 
electrical installation the cost of the distributing conductors is a 
larger-item than that of the generating machinery. This is almost 
always true of long-distance transmission ; and even in an isolated 
electric-lighting plant the wiring is usually more expensive than 
the boilers, engines, and dynamos combined. 

Substantially the same principles apply to all branches of elec- 
trical transmission and distribution, including electric lighting and 
power, telegraphy, telephony, etc. But the subject has been de- 
veloped more thoroughly in the case of electric lighting, which 
requires a more nearly perfect regulation of pressure and current 
than the other applications. 

Measuring Electrical Conductors. — Either the metric system 
or the ordinary English system of units can be employed to meas- 
ure the length and cross-section of wires or conductors.* The for- 
mer system, in spite of its many advantages, is rarely used for this 
purpose in America or in England; and tables or rules employing 
it would be practically worthless at the present time, since they 
must:ultimately be used by common workmen. It should be made 
compulsory before it can be adopted generally. In English meas- 
ure we can select either the mile, yard, or foot as the unit of 
length. The first is too large, as it necessitates inconvenient deci: 
mal fractions; the yard is often employed in England to measure 


* Tables for converting from one system to the other are given in vol. i. pp. 20-22. 


1 


ae EIPOCTRICUWAGCHTING: 


electrical conductors, but it is rarely used for that purpose in 
America, the foot being almost universally adopted as the unit. 
The size of a wire may be stated either in terms of the numbers 
of an arbitrary gauge, or the actual diameter in fractions of an inch 
may be given. Unfortunately the practice of using wire gauges 
has existed from time immemorial, and results in much confusion 
because of the great number of different gauges.* This has been 
overcome to a certain extent in this country by the general adop: 
tion of the Brown & Sharpe, or American wire gauge; but this is 
quite different from the new standard British wire gauge, which is 
used in England. The American wire gauge will be employed in 
the present instance, since in this country wires are made and re- 
ferred to by that gauge very generally; but in many cases it is 
better to specify the actual diameter or cross-section of the wire. 
For this purpose the word mz/ has been introduced, being a short 
name for one thousandth of an inch. That is to say, a wire 100 
mils in diameter is one hundred one thousandths, or one tenth of 
an inch, in diameter. The cross-section of a wire one mil in diam- 
eter is called one czrvcular mil, being the area of a circle one thou- 
sandth of an inch in diameter. Since the cross-section of any 
other round wire will be proportional to the square of its diameter, 
it follows that the cross-section in circular mils can be found by 
multiplying the diameter in mils by itself. We thus avoid the dif- 
ficulty of converting the cross-section into square measure, which 
requires the square of the diameter to be multiplied by .7854 or 
a /4. This is an awkward and unnecessary calculation in the case 
of round wires, it being much simpler and equally definite to meas- 
ure them in terms of a circular unit. For diameters greater than 
46 inch (No. 0000 A.W.G.) it is customary to define the size by 
giving the diameter in mils or the Cross-section in circular mils. 
For example, a solid round conductor one inch in diameter is desig- 
nated as 1,000,000 circular mils. The size of a cable made up of 
a number of strands of wire is given as the sum of the cross-sec- 
tions of the individual strands. Rectangular conductors are meas- 
ured in terms of their breadth and thickness in inches or mils, or 
their cross-section in square mils, which is equal to the product of 
these two dimensions. 

For measuring wires or conductors, a wire gauge or a microm- 

* Wheeler’s Chart of Wire Gauges, W. J. Johnston Co., N.Y., 1887. 


BLECTRICAL DISTRIBUTION. D 


eter may be employed. The former consists of a plate having 
slots in its edge corresponding in size to the gauge numbers. The 
latter is usually a screw-micrometer, which measures the diameter 
‘or thickness in mils, that is, thousandths of an inch. 

Materials for Electrical Conductors. — Copper is the material 
employed almost universally for electrical conductors, on account 
of its high conductivity. The slight superiority of silver in this 
respect 1s more than offset by its higher density and cost. 

There are, however, several metals which are lighter than cop- 
per for the same resistance. For example, aluminum has a con- 
ductivity about one-half that of copper, and its density is 2.7. 

Pete Tne 
339 Sin 0.607, or a 
little more than one-half as much as a copper wire having the same 
length and resistance. Metallic sodium is only about one-quarter 
as heavy as copper for equal length and resistance. 

Although there are several metals that could be used _as elec- 
trical conductors which are considerably lighter than copper, it is 
doubtful if it would be desirable to use them, except in special 
cases where minimum weight is of particular importance, because 
their bulk would be so much greater. For example, an aluminum 
wire must have about twice the cross-section of an equivalent 
copper wire, and would, therefore, require much more insulating 
material to cover it, and would be more clumsy for overhead or 


Hence, an aluminum wire weighs only 


underground conductors or interior wiring. It may be used, how- 
ever, for bare conductors, such as ’bus_ bars, provided its cost is 
low enough. | 

| In addition to metals such as aluminum, which may be em- 
ployed for electrical conductors in place of copper, because they 
are lighter, other metals and alloys are used on account of cheap- 
ness or greater strength. The most prominent of these is iron or 
steel, which until a few years ago was in general use for telegraph 
and telephone lines. But the most recent practice is to employ 
copper even for these purposes; it being found that the lower 
resistance, inductance, and electrostatic capacity (because smaller 
wires are used) more than make up for the increased first cost. 
Iron has rarely been utilized as a conductor in electric light, power, 
or other circuits that carry large currents, because its conduc- 
tivity is much less, being about one-seventh that of copper. An 


4 ELECTRIC LIGHTING. 


iron wire must therefore have seven times the cross-section and 
Tx 7.8 

8.89 
would cost about as much. 

Nearly all alloys have a considerable lower conductivity than 
pure copper, so that they are not very generally used, even for 
overhead conductors. In the latter case, hard-drawn copper wire 
is generally employed, having a conductivity about 2 to 3 per cent 
less than that of annealed copper, and a tensile strength about 
twice as great. The latter is 25,000 to 35,000 lbs. per square 
inch for soft copper, and 50,000 to 70,000 for hard-drawn, the 
lower figure being for large sizes (Nos. 0000 and 000) and the 
higher value for small sizes of wire (Nos. 14 and 16). | 

Electrical Resistance. — In electrical distribution the most im- 
portant factor is resistance, from the scientific as well as from the 
commercial points of view. It entirely determines the flow of a 
direct current, and largely affects alternating-current circuits also, 
necessitating the use of large quantities of copper for conductors, 
the cost of which constitutes the chief item of expense in almost 
all electrical plants or systems, as already stated. 

Resistance appears as a serious difficulty in electrical distribu- 
tion, producing three objectionable effects. First, it causes a advop 
in voltage, so that the various: lamps are not supplied with suf- 
ficient pressure or with the same pressure; second, it involves a 
loss of energy and efficiency ; and third, it produces “eating of the 
conductors, which may destroy the insulation or give rise to 
danger of fire. Each of these effects will be considered separately 


— 6.14 times the weight of an equivalent copper wire, and 


later. 

The determination of electrical resistance can easily be made 
either by calculation or by actual measurement. It is not neces- 
sary here to explain the many well-known ways of measuring 
resistance, such as the Wheatstone bridge and the fall of potential 
methods. These may be found in almost any electrical work. 
Furthermore, it is the usual practice to determine the electrical 
resistance of conductors in electric light and power distribution by 
calculation based upon certain recognized standards. This may 
be verified by tests of samples of the wire or by measurements 
made after the conductors are laid. 

The Standard Conductivity of Copper. — It is almost universally 


BLECIRICAL DISTRIBOTION. i) 


customary to express the comparative conductivity of samples of 
copper in terms of Matthiessen’s standard. Unfortunately, Mat- 
thiessen gave several values which do not AGTCEMCXACULY een 
overcome this. difficulty, a committee of the American Institute 
of Electrical Engineers carefully investigated this question, and 
recommended the general acceptance of a definite value for Mat- 
thiessen’s standard. It is possible to obtain copper of greater 
purity and higher density than that used by Matthiessen, so that a 
somewhat better conductivity of 102 or even 105 per cent of the 
standard may be reached. But practically all commercial copper 
is below Matthiessen’s standard. 

A complete table was prepared by the committee of the Amer- 
ican Institute of Electrical Engineers,* giving the resistance, 
weight, etc., of the various sizes of wire, for both the American 
(B. and*S.) and Birmingham (Stubs) gauges. This table, for 
the A. W. G. and covering wires from Nos. 0000 to 18 inclusive, 
is given on page 8. The resistance of any copper wire at 20 de- 
grees C. or 68 degrees Fahr., according to Matthiessen’s standard, 
10.352 

we 
R being the resistance in international ohms, / the length of the 
wire in feet, and @ its diameter in mils. The latter is easily deter- 


may be calculated by the following simple formula: R = 





mined with accuracy by means of the ordinary screw micrometer. 

A very simple and convenient rule to remember is the fact 
that 1,000 feet of No. 10 A. W: G. wire, which is practically one- 
tenth of an inch in diameter (.1019), has 1 ohm resistance at 20 
degrees C. (68 degrees Fahr.), and weighs 31.4 pounds. <A wire 
three sizes larger, that is, No. 7, has almost exactly twice the 
cross-section and weight per thousand feet, and one-half the resis- 
tance. A wire three sizes smaller, that is, No. 13, has one-half 
the cross-section and weight, and twice the resistance per thousand 
feet. Three sizes smaller than No. 18, that is, No. 16, has one- 
fourth the cross-section and weight and four times the resistance 
of No. 10; and similarly a No. 4 wire has four times the cross- 
section and weight and one-fourth the resistance of No. 10. This 
may be carried to the extreme limits of the gauge in either direc- 
tion, the cross-section doubling with each three numbers. Inter- 
mediate sizes may be approximated by interpolation ; for example, 


* Transactions, vol. x., 1893. 


6 | ELECTRIC LIGHTING. 


one size larger has about 1} (1.261) times, and two sizes larger 
about 14%; (1.59) times the cross-section. The cross-section of 
the next size smaller is always found by multiplying by .798, and 
for two sizes smaller by .629. 

Temperature Coefficient of Copper. — The effect of variations in 
temperature upon the conductivity of copper was given by Mat- 
thiessen * in the following formula : — 


C, = C, (1 — .00387017 + .0000090097?), (1) 


in which C; is the conductivity at any temperature ¢ in Centigrade 
degrees, and C, is the conductivity at zero degrees Cy ~— dinis: ex- 
pression is sometimes converted into one for resistance by merely 
changing signs; but this is incorrect algebraically, since it is neces- 
sary to take the reciprocals of both members of the equation. If 
this is done the following formula is obtained : — 


R, = R, (1 + .0038701¢ + .0000059697?). (2) 


This is usually simplified by reducing the number of decimal 
places, giving the form.: — 


R, = R, (A + .00387¢ + .000005977?). (3) 


In these expressions for resistance, terms containing 7? and 
other higher-powers of ¢ are neglected, hence, they do not give re- 
sults agreeing exactly with Matthiessen’s original formula (Equa. 
1). The correct method is to find the value of the temperature 
coefficient for conductivity (1 — .0088701z + .0000090092?), take 
its reciprocal, which gives the temperature coefficient for resistance, 
then multiply the resistance at 0° C. by this amount in order to 
find the resistance at the given temperature ¢. This is the process 
by which the figures in the table on page 8 were obtained. But 
for moderate ranges of temperature the error resulting from the 
use of Equation 38 is slight, being about } of 1 per cent too high at 
50° C., and about 38 of 1 per cent too high at 80° C. 

Indeed, it is doubtful if any of these somewhat complicated 
formule are actually more correct than the very simply expres- 
sion, — f 

R, = FR, (1 + .0042), (4) 


* Philosophical Transactions, 1862. 
t Electrical World, Feb. 16, 1895. 


ELECTRICAL: DISTRIEBETION. f 


in which, as before, A, is the resistance of a copper conductor at 
the given temperature ¢, and &, is its resistance at 0° C, 

Matthiessen found nearly all pure metals to have substantially 
the same temperature coefficient as copper, the only important 
exceptions being iron and liquid mercury. The values given for 
these are somewhat variable, but are about .0045 for the former, 
and about .0009 for the latter. The temperature coefficients for 
alloys are less than those of pure metals, being only about one- 
tenth as great for German silver as for copper. 3 

The resistance-in ohms of a soft copper conductor at a given 
temperature ¢ in Centigrade degrees may be obtained from the 
following expression :— 


9.586 (1 + .00387¢ + .000005972?) 7 
TERE 1 NT a ee era (9) 
This assumes the ordinary form of Matthiessen’s formula 
(Equa. 3), and gives slightly different results from those set forth 
in the table on page 8, as already explained. 
The very simple expression, — 


ki= 


pr, = 280 aU 4G 





gives values agreeing exactly with Matthiessen’s original formula 
at 23° C., and not differing by more than two-tenths of one per 
cent between 0° and 85° C., which covers the ordinary tempera- 
ture range of conductors used in electrical distribution. At 60° 
C., which is the usual heating limit allowed in electrical machin- 
ery, the results obtained from Equation 6 are three-quarters of 
“one per cent less than those of Matthiessen. This expression is 
therefore sufficiently accurate for almost any practical calculation. 

In fact, the variation in resistance of copper is so great with 
ordinary changes in temperature that it is rarely possible to pre- 
determine it with great accuracy. The temperature of an over- 
head line may vary from natural causes enough to alter the resis- 
tance about 25 per cent. A further increase due to the heating 
effect of the current would make a total change of about 40 per 
cent in resistance. Underground and interior conductors are not 
subject to such extreme variations in the temperature of their 
environment, but they often amount to many degrees, particularly 
for the latter; and the heating effect of the current may be equally 


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MLEGTRICAL DISTRIBUTION. 9 


great. Fortunately, however, in electrical transmission or distri- 
bution the current does not ordinarily heat wires more than 5 or 
10 degrees, the loss of voltage being usually the controlling factor. 
Under the head of current capacity the rise in temperature of the 
various kinds of conductors will be discussed later. 

In any given case the probable temperature around a conductor 
and the rise due to the current can be at least approximately de- 
termined, so that resistance calculations can be made accordingly. 

It is customary to specify in plans and contracts that copper 
for electrical purposes shall have a conductivity not less than 98 
per cent of Matthiessen’s standard. In some cases only 96 per 
cent is required; but it should not be allowed to fall below this 
limit, as it is perfectly practicable to obtain copper of such quality, 
and inferior grades would not be enough cheaper to make up for 
their lower conductivity. Allowance should be made for this fact 
in calculating the resistance of conductors. 

The Drop, or Lost Pressure in Volts. — This is the first effect 
of resistance in electrical distribution, and is very easily and defi- 
nitely determined from Ohm’s law by changing its ordinary form 
7=— 2) into # = /K.> This is not only true of the whole cir- 
cuit, but also applies to any portion or branch of the circuit ; and 
ordinarily it is far simpler and more likely to avoid errors if each 
part of the circuit is considered separately. In the case of a very 
complicated electrical: system, it would be practically out of the 
question to treat the circuit as a whole; but it is always possible to 
divide the system of conductors into separate lengths, in each of 
which we can determine the current, the resistance, and therefore 
the fall of potential which takes place. In most practical work the 
current in amperes is given, since it is usually known how many 
lamps or how much power are to be supplied. It then becomes 
necessary to calculate the value of the resistance in order to have 
the proper value for the drop, the latter being assumed or fixed by 
the conditions in each case. The common idea that a short con- 
ductor of very large diameter has no appreciable resistence is quite 
fallacious. For example, a bar of copper one foot long and one 
inch in diameter has about one hundred-thousandth of an ohm re- 
sistance. While this may be a negligible amount in most cases, 
it is always perfectly definite, and is often quite appreciable. Such 
a rod would carry one thousand amperes with a drop of one hun- 


19 ELECTRIC LIGHTING. 


dredth of a volt between its ends, or ten volts per thousand feet, 
which is by no means insignificant. Bars of this size or larger are 
often used in practice carrying correspondingly heavy currents ; 
hence it is not safe to ignore resistance, even in the case of very 
large conductors. 

Loss of Energy. — The second objectionable effect which re- 
sistance produces in electrical distribution is the loss of energy’ 
which it occasions. This loss is absolute, and must always occur 
whenever a current flows through a resistance. The exact value 
of this loss is given by the expressions : — 

fe? 


Watts lost, = 1A Bie 


in which / is the current in amperes, 7 is the resistance in ohms, 
and £& is the drop or lost.pressure in volts, being applicable either 
to the whole circuit or to any part of it. From one of these ex- 
pressions the loss of energy can always be ascertained, provided 
any two of the three quantities are known. These equations give 
the loss which occurs continuously so long as the current flows ; 
that is, the vate of dissipation of energy or the power wasted. 
For a given time ¢ in seconds — 


i? Lt 
Loss of energy (in joulés or watt-seconds) = 7 *A7—= 2 77 == 





To find the loss of energy in heat units, any of the above values 
may be multiplied by .24 for calories (gram-degree cent.), or by 
.00095 to obtain British thermal units (pound-degree Fahr.). 
This loss of energy, while quite considerable in almost every 
electrical system, usually amounting to from 5 to 25 per cent, is | 
rarely the controlling consideration in electric lighting. The dof, 
which has already been considered, and the heating limzt, which 
will be discussed later, are usually of more consequence than the 
mere waste of a small fraction of the total energy, the success or 
failure of an electric lighting plant being dependent upon keeping 
them. within certain limits. | 
Economy in Design of Conductors. In many cases, particu- 
larly for long-distance transmission in contradistinction to local 
distribution, the relation between the first cost of the conductors 
and the energy lost in them may be a matter of prime importance. 
This subject was first attacked in 1881 by Lord “elvin, then Sir 


PLeCLTIGAL LIS 7KIBU LION. idl 


William Thomson, who read before the British Association a paper 
on “The Economy of Metal Conductors of Electricity,” in which 
he attempted to give a general solution of the problem. The con- 
clusion reached by him, and now known as “ Kelvin’s Law,” may 
be stated in the following language: The most economical size of 
conductor ts that for which the annual interest on capital outlay 
equals the annual cost of energy wasted. In other words, the total 
annual expenditure for interest on the investment and energy lost on 
the line 1s a minimum when these two ttems are equal to each other. 

The importance of this law has usually been greatly overesti- 
mated, but gradually its hmitations have been brought out. In 
1886 Professors Ayrton and Perry showed, in papers before the 
Society of Telegraph Engineers and Electricians, that Kelvin’s 
Law applies only in certain cases ; and they gave various modifica- 
tions and extensions of it. Professor George Forbes has also con- 
tributed to this subject in his Cantor Lectures of 1885,* in which 
he showed that the portion of the investment which is not propor- 
tional to the cross-section of the conductor should be kept separate, 
so that the amended law becomes: Zhe most economical area of 
conductor ts that for which the annual cost of energy wasted ts equal 
to the annual interest on that portion of the capital outlay which ts 
proportional to the area or weight of metal used. Professor William 
A. Anthony, in an article on “ Economy in Conductors, and the 
Limitations in the Applicability of Kelvin’s Law,” + demonstrates 
that in some cases Kelvin’s Law gives absurd results, and' may, 
for example, require that a// of the energy should be wasted tn order 
to secure the highest economy. This is due to the fact that the 
minimum expense of operation is considered, and the energy deliv- 
ered at the end of the line, which is still more important, is entirely 
ignored. In fact, a great many laws of this kind can be deduced 
according to what factors are considered. 

Kilgour ¢ and Abbott § give 15 possible combinations of the 
six variable factors involved in the problem, but state that only 
11 of these are likely to be of any practical importance. The six 
factors and the 11 cases are as follows: 


-* London Liectrician, vols. xv. and xvi. 

+ Electrical Engineer (N. Y.), Oct. 31, 1894. 

t Electrical Distribution, London, 1893, p. 115. 

§ Electrical Transmission of Energy, N. Y., 1895, p. 457. 


Te, ELECTRIC. LICHIING: 


- 


V = the pressure at'the receiving end of the conductor ; 

v = the pressure at the delivering end of the conductor; 
W = the power given to the receiving end of the conductor; 

zw == the power obtained at the delivering end of the conductor ; 
/ = the current in amperes, and 

SS = the cross-section of the conductor. 


CASE NO-e GIVEN. REQUIRED. CASE NO. GIVEN. REQUIRED. 
iJ eee a Ly hls 20, Se . nine Veit 
2 Naan & v7, W,w, S. 8 1 SES. V, Daal, aes 
3 V, w. WAT AE , as 9 W, w. V, Ula 
.4 VS v, 1, W, w. 10 WES. Viv, I, w. 
5 OF: View Oh aos 11 w, S. Vo 0 ERG 
6 v, W. Ped, Wye: 


This is a far more complete treatment of the question than 
that originally given, Kelvin’s Law being only one (No. 5) of 
these 11 different cases. But any of these solutions of the prob- 
lem is of somewhat doubtful practical value; and it is probably 
true that Kelvin’s Law, or any modification or extension of it that 
has yet been brought out, has done more harm than good in elec- 
trical engineering. It gives a false confidence in the results of 
calculations which may be totally at variance with real commercial 
economy. The reason for this difficulty lies chiefly in the fact that 
the actual costs of some of the items cannot be expressed, even 
approximately, as mathematical functions. Furthermore, various 
incidental factors and particular conditions arise, such as the avail- 
able sizes of machines, which render a general solution of this 
problem of questionable value in the actual cases which are found 
in practical work. 

It is a common mistake to forget that the interest and depre- 
ciation on the investment is a fixed and irretrievable expense, 
while the energy lost on the conductor depends upon the power 
transmitted. When the plant is lightly loaded, or is shut down 
entirely, owing to hard times, strikes, etc., the fixed charges run 
on as usual, but the energy loss is greatly reduced, or stopped 
altogether. Hence it is not wise to lay the full amount of copper 
corresponding to the maximum or even ordinary demands, as there 
is no control over the investment after it is once made, whereas 
the energy loss adjusts itself to the working conditions, 

Probably the safest, as well as the quickest, method to arrive 
at a correct result would be to obtain a general solution of the 


PREGURICAL  DISTRIBEGTION 13 


problem by means of some form of Kelvin’s Law; then this re- 
sult should be carefully checked by assuming a larger and also a 
smaller wire, and estimating the economy that would be secured 
if they were substituted for the size of wire obtained by the calcu- 
lation. The difficulties of determining the various items of ex- 
pense are greatly reduced by assuming a certain size of wire, and 
the several factors that are almost impossible to cover by a gen- 
eral formula, immediately become definite. Scientific and rational 
methods should always be preferred to empirical ones; but every 
experienced engineer will admit that when complicated questions 
of cost arise it is unwise to rely entirely upon general formule, 
which are almost necessarily abstract and incomplete. The at- 
tempt to force science beyond its legitimate limits has done great 
injury to many industrial enterprises as well as to science itself. 

Specific examples of this problem will be considered later in the 
case of constant-current arc-lighting circuits and feeders for con- 
stant potential systems. 

Current-Carrying Capacity of Conductors. — The third objec- 
tionable effect of resistance in electrical distribution is the heating 
which it causes. The production of heat in an electrical conduc- 
tor has already been stated in terms of the various quantities in- 
volved. This heat is an absolutely definite and unavoidable result 
cmethestowsottie. current. [ts etiect, is to. raise the tempera- 
ture of the conductor, and this rise continues until the rate at 
which heat is lost equals the rate at which it is generated; then 
the temperature becomes constant. It is obvious, therefore, that 
any electrical conductor is only capable of carrying a certain cur- 
rent with a given elevation of temperature, and in practical work 
the allowable temperature is limited by considerations of injury to 
insulation, danger of fire, etc. No exact general rule for current 
capacity can be given, as much depends upon the conditions in 
each case. But, since a wide margin must be allowed between the 
danger point and the permissible current capacity, it is possible 
to establish rules which are somewhat arbitrary, but sufficiently 
safe in almost any case. This is practicably the basis upon which 
tables are made giving the current that it is allowable for any size 
of wire to carry. These tables are partly based upon general 
experience, and partly the results of experiment and calculation. 

The first rule of this kind originated with Lord Kelvin, and 


14 BEBOCTRICOLIGIUT ING: 


was adopted by the Board of Trade (London). It stated that the 
current density in copper conductors should not exceed 1,000 
amperes per square inch of cross section. 

Professor George Forbes discussed this problem in a paper 
read before the Institution of Electrical Engineers (London) in 
March, 1884, and showed that the Board of Trade rule was hardly 
safe for very large conductors, and gave an unnecessarily large 
margin for small wires. This fact is very evident when it is con- 
sidered that the current at a given density and also the heating 
increase in proportion to the square of the diameter of a wire, 
while the heat-dissipating surface only increases as the diameter. 

Dr. A. E. Kennelly has given the results of his investigations 
in two papers before the Association of Edison Illuminating Com- 
panies, Aug. 18, 1889, and Aug. 11, 1898.* He determined by 
calculation and experiment the heating of conductors submerged 
in water, buried in the earth, inclosed in wooden molding, and 
suspended in air. 

It is found that there is not such a great difference between 
the heating effects under these various conditions. An insulated 
cable in water is the simplest case; since the rise in temperature 
of the conductor depends merely upon the thermal resistance of 
the insulation, the outer surface (or sheathing) of the latter being 
kept at a constant temperature by the water. An underground 
conductor only differs from the foregoing in the fact that its 
sheathing may rise in temperature because heat is not taken from 
it rapidly enough by the surrounding soil or conduit. In other 
words, the thermal resistance of the conduit and soil is added to 
that of the insulating covering. For underground conductors in 
iron pipe conduits laid in cement, the temperature elevation due 
to this cause would be small, probably not more than 10 or 20 
per cent greater than that of the same cables submerged in water. 
The heating of conductors in wooden or even earthenware con- 
duits would be considerably greater, and in the case of the former 
might be considered to be the same as for those placed in wooden 
panels or molding, the rules for which will be given later. Insu- 
lated wires suspended in air are more highly heated than similar 
submarine or most underground conductors, for the reason that 
the thermal losses by radiation and convection through the air are 


* Electrical World, Nov. 23 and 30, 1889 and Sept. 2 and 9, 1893. 


ELECTRICAL DISTRIBUTION. 15 


less than those through water and solid bodies, except those which 
are very poor conductors of heat, such as wood. For similar rea- 
sons the temperature rise of a bare wire in air is usually greater 
than that of the same wire covered with insulating material. The 
effect of the latter is to increase the surface from which heat is 
radiated and carried away by convection. In most cases a con- 
siderable increase in the temperature of a bare wire is not objec- 
tionable .except so far as it represents loss of energy. The real 
limitation to the heating of electrical conductors is the point at 
which their insulation is likely to be injured. 

The following are standard tables, giving the maximum current- 
carrying capacity of different sizes of insulated copper conductors : 


TABLES, Of.) CURRENT =—~CARRVINGSCAPACITY. 


TABLE 1. TABLE 2. TABLE 3. TABLE 2. TABLE 3. 

A. W. Ge AMPERES. AMPERES. AMPERES. CIRCULAR MILLS. AMPERES. AMPERES, 
18 3 3 5 200,000 200 300 
16 5 6 8 300,000 270 400 
14 10 12 16 400,000 330 500 
12 15 17 23 500,000 390 590 
10 20 24 32 600,000 450 680 
8 25 a8 46 700,000 500 760 
6 35 46 65 800,000 550 840 
5 45 54 77 900,000 600 920 
4 50 65 92 1,000,000 650 1,000 
3 60 16 110 1,100,000 690 1,080 
2 70 90 131 1,200,000 730 14150 
1 85 107 156 1,300,000 70m 1,220 
0 100 127 185 1,400,000 810 1,290 
00 120" = 9 150 220 1,500,000 850 1,360 
000 145 177 262 1,600,000 890 1,430 
0000 175 210 312 1,700,000 930 1,490 
1,800,000 970 1,550 
1,900,000 1,010 1,610 
2,000,000 1,050 1,670 


Table No. 1 is based upon Kennelly’s experiments, and is in- 
tended to allow a rise in temperature of 75° F. for twice the cur- 
rent specified, thus giving an ample factor of safety. The normal 
current would only raise the temperature 18%° F., since the heating 
effect is proportional to the square of the current. The National 
Electrical Code permits a current density 20. to 25 per cent 


greater than the foregoing, the figures being given in Table 2. 


16 ELECTRICWIGATING. 


This would give a temperature elevation of 27° to 30° F., and still 
allows a considerable increase (about 60 per cent) in current 
above the rated value without injurious effects. This applies to 
rubber-covered wires, which should never be heated above 150° F., 
and should have a normal working temperature considerably below 
this limit, in order to have a margin for safety. Table 3 permits 
a still greater current density, and is used for wires with “ weather 
proof” insulation, which is not so susceptible as rubber to injury 
by heat. 


BIBLIOGRAPHY OF ELECTRICAL TRANSMISSION AND DISTRIBUTION, 


INCLUDING OVERHEAD AND UNDERGROUND CONDUCTORS AND INTERIOR WIRING. 


ABBOTT, A. V., Electric Transmission of Energy, N.Y., 1895. 

Bapt, F. B., Zucandescent Wiring Handbook, Chicago, 1894. 

BELL, Louis, -lectric Power Transmission, N.Y., 1897. 

Davis, C. M., Standard Tables for Electric Wiremen, N.Y., 1896. 

HERING, CARL, Universal Wiring Computer, N.Y., 1894. 

Kapp, G., electric Transmission of Energy, London, 1894. 

KILGOUR, SWAN, AND BiaGs, Electrical Distribution, [ts Theory and 
Practice, London, 1898. 

No.1, A., How to Wire Buzldings, N.Y., 1893. 

RAPHAEL, F. C., Localization of Faults in Electric Light Mains, N.Y. 
and London, 1897. 

Ross, R., Llectric Wiring, N.Y. and London, 1896. 

RUSSELL, S. A., Hlectric Light Cables and the Distribution of Electricity, 
London, 1892. 

WATSON, A. E., Handbook of Wiring Tables, N.Y., 1892. 

WEILLER ET VIVAREZ, Lignes et Transmissions Electriques, Paris, 1892. 


SERIES SVSTEMS OF ELECTRICAL DISTRIBUTION. Ay 


Cua rrside: 1s Agee idl 


SERIES SYSTEMS OF ELECTRICAL DISTRIBUTION. 


THE various systems of electrical transmission and distribution 
are Classified in the following table. They are especially selected 
with reference to their use in electric lighting; but they include 
those employed for power transmission and other electrical pur- 
poses, the same principles and methods being generally applicable. 


SYSTEMS OF ELECTRICAL DISTRIBUTION. 


DERIES SYSTEMS, 


Constant Current. Voltage usually varied. Direct Current. 


Series arc lighting. 
Usually operated at about 10 amperes and 50 volts per lamp. 
Series incandescent lighting. 
About 10 amperes and 10 to 380 volts per lamp (about 3 candle- 
power per volt). 
Series incandescent lighting (“ Municipal systems ”’). 
Three to 3.5 amperes and 20 to 50 volts per lamp (1 volt per candle- 
power). 
Series-parallel incandescent lighting. 
Similar to No. 2, but single lamps replaced by groups in parallel. 


Direct current-converter systems for incandescent or arc lighting. 
Motor-dynamos in series, lamps supplied by secondary circuits, 


Alternating Current, 


6, 7, 8, 9, and 10. Alternating current systems corresponding to Nos, 1, 


2,3, 4, and 5. 


PARALLEL SYSTEMS. 


Constant Potential. Current varies with number of lamps. Direct Current, 


II. 
12. 
13. 
14. 


Two-wire incandescent and arc lighting (about 110 or 220 volts). 

Three-wire incandescent and arc lighting (about 220 or 440 volts). 

Five-wire incandescent and arc lighting (about 440 volts). 

Two-wire with motor converters in parallel (primary 1,000 to 5,000 
volts). 


18 BPLECTRIC LIGHTING. 


Single Phase Alternating Current. 


15. Low tension incandescent and arc lighting without transformers. 
This corresponds to No. 11. Other alternating current systems 
similar to Nos. 12, 18, and 14 have not been introduced. 
16. High-tension incandescent and arc lighting with transformers. 
Primary circuit 1,000 to 5,000 volts, two- and three-wire secondary 
circuits at about 50, 100, or 200 volts. 
17. Very high tension systems with step-up and step-down transformers. 
Long distance transmission circuit 5,000 to 25,000 volts. 


Polyphase Alternating Current. 
18. Two-phase system. 
19. Three-phase system. 
20. Monocyclic system. 


For the sake of completeness, the above table includes almost 
every possible system of electrical distribution, but many of them 
are unimportant or entirely obsolete at the present time. The 
systems which are now more or less generally used are Nos. 1, 11, 
12,13, 14, 46317, 8, 1O;-and/s202 ) Uhevlastethrcesare tprimamin 
intended to operate motors, but are also employed in many cases 
for electric lighting. 


SERIES SYSTEMS OF DISTRIBUTION. 
The simplest arrangement of lamps or other devices to be sup- 


plied with electrical energy is a series system in which the cur- 
rent from the + terminal of the dynamo, J, passes first through 





Fig. 1. Series Arc Circuit. 


one lamp, Z, and then through another, and so on, finally returning 
to the — terminal of the dynamo, as shown in Fig. 1. In such 
cases the current is usually constant, hence the expression constant 
current is practically synonymous with sevzes in electrical distribu- 


SERIES SYSTEMS OF ELECTRICAL DISTRIBUTION. 1) 


tion. The term igh tension also applies, since the voltage usually 
employed is high, being equal to the sum of the pressures con- 
sumed in all of the lamps on the circuit. For example, sixty 
lamps are commonly placed upon a single arc-lighting circuit ; and 
since each lamp (open arc) requires about fifty volts, it follows 
that the total pressure approximates 3,000 volts. The problem of 
designing or studying series circuits is not difficult, the path of the 
current being usually simple, and the current constant throughout 
the circuit. This last statement is only true, however, if the leak- 
age of current is insignificant, which is generally the case in elec- 
tric light and power distribution. 

Distribution of Potential on Series Systems. — The potential on 
a series system falls throughout the circuit in direct proportion to 
the resistance. That is, E=/R, the difference of potential £ in 
volts between any two points being equal to the product of the 
current / in amperes and the resistance # in ohms included 
between them. This simple fact completely covers any possi- 
ble problem that can arise in connection with a series system, pro- 
vided a direct current is used, and is easily applied in almost any 


L ib u 
~ MA 
a 
¢ 
i] 
e R 
M 
Gia 
! : 
: 
P Q 


Fig. 2. Distribution of Potential on Series System. 


case. In Fig. 2 an arc-lighting system is represented, D being 
the dynamo and Z, Z, Z, the lamps, connected in series. The total 
difference of potential generated by the dynamo is assumed to be 
1,000 volts, measured between the two brushes marked + and —. 
This potential falls as the current traverses the circuit, fifty volts 
being consumed by each of the twenty lamps. This is made up 
of forty-five volts actually used in the lamp itself, and a drop of 
five volts on the conductor between two lamps. That is, the drop 
on the line wire is usually about 10 per cent of the total AJIZF. 
The relative potential of the various points on the circuit is easily 


20 ELE CERI CHIIGHIING. 


found. For exampie, between the + brush and the middle point 
M of the circuit, there is a difference of potential of 500 volts, and 
the same amount between the middle point and the — brush. 
Similarly any two points on the circuit will have a difference of 
potential equal to fifty volts, multiplied by the number of lamps 
included between them. 

Personal Danger from Series Circuits. — If a man standing on 
the ground touches a very highly insulated circuit, only a very 
slight current will pass through his body; but if the insulation is 
low or any defect exists at any particular point, then a considerable 
current may flow through his body. In Fig. 2 the line is supposed 
to have a ground connection at the point /, due to a defect in the 
insulation. This will cause the potential of the circuit to be zero 
at that point ; consequently a man may stand on the ground, and 
touch the line at that point with perfect impunity. If he touches 
the wire at point Q he will receive a barely perceptible shock, due 
to 100 volts, since there are two lamps between that point and the 
ground connection; but if the circuit be touched at the point X&, 
the difference of potential between it and the ground connection 
being 18 x 50 = 900 volts, will produce a dangerous, or perhaps 
fatal, current. When the defect in the insulation does not amount. 
to what is called ‘dead ground,” but has a resistance, for example, 
of 1,000 ohms, then a man touching the wire at the point & will 
receive a shock due to 900 volts as before; but the resistance of 
the ground connection, which is 1,000 ohms, will be in series with 
his body. Consequently the current will be less; and, assuming 
the resistance of his body to be 1,000 ohms, the current will be 
one-half as great as in the first case. If the ground connection 
has a resistance of 8,000 ohms, the current through the body would 

900 i} 
be = 

8,000 + 1,000 10 
We may sum up these various cases as follows : — 

1. A very highly insulated direct-current electrical circuit may 
be touched at any one point without danger by a man standing on 


of an ampere, which is not dangerous. 





or in connection with the ground. 

2. If a ground connection exists on a series electrical circuit, 
the danger of touching the circuit increases directly with the resist- 
ance between the ground connection and the point of contact. 

3. The resistance of the ground connection is in series with 


Dirt OS wists OF ELECTRICAL DISTRIL ULION, 21 


the body of any one connected with the ground and touching the 
wire at some other point. 

4. It is never safe, however, to assume the insulation to be 
perfect, or that a ground connection exists at some particular 
point, or that it has a high resistance. The circuit should always 
be treated as if the most dangerous possible conditions existed. 

Regulation of Series Systems.— The condition required on 
series circuits is usually the maintenance of a constant current. 
This is accomplished by designing the dynamo so that it will 


automatically generate a nearly constant current. The various 


| 


J 


Me) 


dynamos used in series arc-lighting, such as the Brush, Thomson- 
Houston, and Wood machines, are well-known examples of this 
type of generator. They are provided with regulating devices, 
which either shift the brushes or vary the strength of the field, 
OL (DC ming Ordersto keep rthe current, at«a, constant value. In 
addition to these special regulators, such machines are so designed 
that they have considerable self-induction, resistance, and armature- 
reaction, all of which tend to prevent the current from rising to 
a high value, even when the machine is short-circuited.* 
eries Arc-Lighting System. — The general arrangement of the 
apparatus and circuit is represented in Fig. 1. The dynamo and 
lamps may be selected from the various well-known and thoroughly 
successful forms of constant-current arc-lighting apparatus. The 
determination of the proper size of wire is not very difficult. Gen- 
eral custom and considerations of strength require that no wire 
smaller than No. 8, A. W. G., should be used. Similarly it would 
not usually be necessary to employ a conductor larger than No. 4, 
because the potential being high, and the current small, the loss of 
\energy is not great, even in a wire several miles in length. To 


# NG ; G A 5 
‘\ take a specific case, let us assume a circuit five miles long, supply- 


Xe 


ing 80 arc lamps, the potential being 4,000 volts and the current 
10 amperes. If No. 6 wire is used, the resistance would be 2.1 
ohms per mile, or 10.5 ohms for the whole line. This involves 
a drop of 105 volts and a loss of energy of 1,050 watts, which is 
only 2.63 per cent ; consequently it is evident that the use of a 
little larger or a little smaller wire would not seriously affect the 
economical working of such a line. The substitution of No. 3 
for No. 6 wire would save one-half the loss of energy, the cross- 


* For a description of such machines see Vol. I., p. 330. 


Fag ELECTRICAIAGHLING 


section and weight being twice as great, and the cost of the insu- 
lated conductor would be nearly doubled. With No. 6 wire the 
total weight of copper would be 2,098 pounds, and the cost of the 
wire (insulated) would be about $500. It is doubtful if it would 
be wise to invest an additional $500 in order to use No. 3 wire 
and save one-half the energy or 025 watts. 

The New Brush Arc-Lighting System is an interesting case 
of series distribution. In the original type of Brush dynamo the 
armature is provided with two or more separate open-coil windings, 
connected to a corresponding number of commutators. ‘The cir- 
cuit leads through these windings in series, so that the construc- 
tion may be regarded as equivalent to several armatures in series. 


P 7+ 3000 


C 
2000 





— 3000 
Fig.4. 


Figs. 3 and 4. Original Arrangement of Brush Are Lighting System. 


This arrangement is represented diagrammatically in Fig. 3, in 
which A, #, and C are three commutators connected in series with 
each other and with the line that supplies a number of lamps, 
L, £, etc., in the usual manner. Assuming each armature wind- 
ing to generate 2,000 volts, the total £.47/ of the machine will 
be 6,000 volts. The distribution of potential in this case is shown 
in Fig. 4, the + brush of C being + 8,000 volts, and the — brush 
of A being — 8,000 volts, with respect to the potential of the 
eatth, which as’ represented ‘by thegzero line "COs welnesiallvor 
potential through the circuit is indicated by the inclined lines, P O 
and O WN, the total amount being 6,000 volts, and the middle point 
being zero. This assumes an ideal case with a uniform distribu- 
tion of conductor resistance and insulation resistance, but would 


SERIES SVSTEMS OF ELECTRICAL DISTRIBUTION. aes 


be approximately true for a practical case in which the system was 
in good condition. If the insulation of some portion of the circuit 
became poor, it would 
_- tend to make the poten- 
tial at that point ap- 


P.+6000 
G 
; 2000 
proach zero, producing 
a corresponding change B 
in the rest of the cir- 2000 
Cll sHOmsexampic.. a 


ground connection at ei 
the negative terminal VV 0 
would bring that point N 

Fig. 5. Distribution of Potential with Grounded 


+to zero, and the positive 
: Terminal. 

terminal P would then 

become + 6,000 volts, as represented in Fig. 5. 

The new Brush system, illustrated in Fig. 6, differs from the 
old in the fact that the lamps, Z, Z, are inserted in the circuit 
between the commutators 4, A, and C, in which case the line con- 
sists of three loops. With this arrangement, the .J/F. generated 


by each of the three armature windings is consumed by the lamps 





Fig. 6, Fig.7, 


Figs. 6 and 7. New Arrangement of Brush Arc Lighting System. 


between it and the next armature winding, so that the potential 
does not rise above + 1,000 volts, or fall below — 1,000 volts, in 
the ideal case represented in Fig. 7. Even if the circuit becomes 
grounded at any point, the potential will nowhere exceed 2,000 
volts, and the maximum difference of potential existing between 
any portions of the circuit will not be greater than this amount. 
A voltmeter connected across from the — brush of B to the + 
brush of C would only indicate 2,000 volts, in spite of the fact 
that the £.17.F. generated between those points is 4,000 volts, the 


24 ELECTRICALIGHIING: 


remaining 2,000 volts being used in the lamps between B& and C. 
This reduction or subdivision of the total £.47.F; is the advantage 
of this system, and avoids the dangers involved in the use of the 
ordinary types of machine for supplying a large number (50 to 
200) of arc lamps in series. On the other hand, it is necessary 
to arrange the line in several loops instead of having one long cir- 
cuit. In Fig. 6, for example, there would be six wires running 
out from the station, while Fig. 8 would only require two. Never- 
theless, the former plan may be preferable. to the operation of 
three separate dynamos, which would be less efficient, occupy more 
space, and demand more attention than a single large machine. 

If desired, the number of Jamps on any loop may be increased 
or decreased, since the current is kept constant by’a regulator on 
the dynamo; and it is quite immaterial where the resistance is 
introduced in a series circuit. In fact, any or all of the lamps may 
be cut out, or they may be put upon two loops and none on the 
third, or the full load may be placed on a single loop, in which 
case the arrangement reduces to the ordinary one shown in Fig. 3. 
When the number of lamps on any loop is augmented or diminished, 
the potential difference between its terminals varies in direct pro- 
portion, so that two-thirds of the lamps on one loop would require 
a P.D. of 4,000 volts between the brushes to which it is connected. 
This gives great flexibility to the system, and provided the lamps 
are not very unequally divided, the pressure is not excessive on 
any one loop. It should be noted that in either the old or the 
new system, the full /.JZ.F. of 6,000 volts would be found to exist 
if the circuit be opened at any point. Indeed, the P.D. would 
tend to rise momentarily considerably above the normal voltage.* 

Series Incandescent Lamps on Arc Circuits. — Several forms of 
incandescent lamps have been designed and manufactured for use 
on the regular 10-ampere arc circuits. These consist of lamps 
similar in general principle and construction to those used for con- 
stant potential, parallel distribution, but containing a shorter fila- 
ment of larger cross-section that is sufficiently heavy to carry the 
full current of 10 amperes. 

The most important consideration is that of maintaining the 
continuity of the circuit when the filament of any lamp happens to 
break, which might occur at any time. This may be accomplished 


* Volalwep eget. 


nie lesestolLiis OF ELECTRICAL DISTRIBUTION. 25 


by some form of cut-out, which short-circuits the lamp when the 
filament is broken. One type of this device is called a “film cut- 
out,” and consists of a thin sheet, /; of paper or other material 
interposed between the points P and P connected to the conduc- 
tors 4 and & which enter and leave the lamp, as represented in 
Fig. 8. This film obliges the current to 
pass through the lamp so long as the fil- 
ament is intact; but when the latter 
breaks, the difference of potential rises 
from its ordinary value of 10 or 20 volts 
to the full A.AZF. of the circuit, which 
is usually several thousand volts. This 
high pressure is sufficient to puncture 
the film, allowing the current to pass di- 
rectly across between the points P and Pa ee ae 
P, thus short-circuiting the lamp and re- descent Lamp. 
establishing the continuity of the circuit. 

In some cases a small automatic switch is employed, which is 
caused to close and short-circuit the lamp by means of a magnet 
connected across as a shunt between the leads of the lamp. The 
coils of this magnet are of high resistance, and carry little current 
until the filament is broken, when the full current is thrown 
through them, causing the switch to close. 

‘¢ Municipal’? Series Incandescent Lighting Systems. — These 
are similar to the preceding; but instead of operating with a’stan- 
dard arc-lighting current of 10 amperes, they are usually designed 
for about 8 or 38.5 amperes. This gives a filament of sufficient 
length and cross-section to be durable, and yet does not require 
excessively large leading-in wires. The lamps are made of various 
sizes, requiring about one volt per candle-power. The practice 
with this system is to feed the circuit with a constant potential, 
usually from 590 to 1,000 volts, several of such circuits being or- 
dinarily operated in parallel by the same dynamo, YD, as represented 
in Fig. 9. This arrangement is therefore a parallel-series system. 
When the filament of a lamp breaks, and it is automatically cut 
out of the circuit, the current increases in strength, since the total 
resistance is reduced, the potential remaining constant. This in- 
crease of current is indicated by an ampere meter, or current indi- 
cator 4 placed in each circuit, and is corrected and brought back 





Fig. 8. 


26 ELECTRIC LIGHTING. 


to its normal value by switching in an extra or “relief” lamp Z,, at 
the station. This is usually done by an attendant who is kept on 
duty to watch the various circu:ts. The system is rather a crude 
one, and is rarely used except for street-lighting in place of arc 
lights where the more powerful light of the latter is not required. 
Either the direct or alternating current is applicable to this method 
of distribution, and both have been used. ‘The current capacity 
of the dynamo must be sufficient to supply the various circuits in 
parallel. In the case shown (Fig. 9), the current required would 
be 15 amperes, since there are 5 rows of lamps, each taking 3 am- 
peres. With 10 lamps of 50-candle-power and 50 volts in series, 
the dynamo should operate at a constant potential of 500 volts. A 
shunt or compound wound direct current machine, or a separately 
excited or composite alternator, would be suitable for the purpose. 





ee eM eo ke te le 
[ 24O-O-O-O0-0-0-0-0-0-O7F] 4 & 
E}-0-0-0-0-0-0-0-0-0-0 9.75. 
, [| -}-O-O-O-O-O-O-O-O-O-O i 
DO eo 
fA Se / 





ke 


Fig. 9. Parallel-Series System of Distribution. 


In the case of the compound or composite machines they should ~. | 
; {= 


simply give an absolutely constant potential, since the number of | 
lamps, and therefore the drop, on each circuit is constant. 

Series-Parallel Incandescent Lighting Systems may be arranged 
in the manner indicated in Fig. 10. Several lamps are arranged 
in parallel to form a group, and a number of such sets are con- 
nected in series, as shown. It is not necessary for the groups to 
be identical, provided they are all adapted to take the same current 
in amperes, which should be kept constant, and provided the 
lamps of each set agree in voltage. For example, on the ordinary 
10-ampere arc circuit, one group might consist of 5 lamps, each 
requiring 50 volts and 2 amperes; the next might be composed of 
10 lamps, each taking 100 volts and 1 ampere, and so on. 

Such groups have been used directly on the ordinary series arc- 
lighting circuits (constant current), like the series incandescent 


4 Aan 
i 


£ 


SLRIES SYSTEMS OF ELECTRICAL DISTRIBUTION. 27 


lamps described on page 24. The former arrangement is even 
less practical than the latter, and is also inferior to the “muni- 
cipal”’ system, since a lamp which breaks or burns out cannot be 
either short-circuited or compensated for by adding a lamp in the 
station. To provide for this contingency, which is likely to be 
of frequent occurrence, a local device ds required for each group, 
which will either connect fv new, Jan Payee ia sone of the 





Fig. 10. Series-Parallel System of Distribution. 


lamps fails, or short-circuit the entire group. This is such a com- 
plicated and unreliable arrangement that the system is not a very 
practical one. 

Alternating Current Series Systems. — Each of the direct cur- 
rent series systems that have been described has, or at least might 
have, a counterpart alternating current system. The general 
arrangement and method of operation would remain substantially 
the same; but as the phenomena of alternating currents differ 
in some respects from those of direct currents, the discussian of 
such systems will be given in the chapters on Alternating Current 
Distribution. 


28 ELECTRICAINGH TING. 


en CE Agmaue Ra Tt 
PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 


In contradistinction to the series connection of lamps or other 
devices to be supplied with electrical energy, the other common 
method of distribution is the favallel or multiple arc arrangement 
represented in Fig. 11. Assuming that four lamps, each taking 
one ampere, are to be fed, the current generated by the dynamo D 
should be 4 amperes, which divides at the point where the first 
lamp is connected, and 1 ampere flows through it. The remaining 
3 amperes pass on to the next lamp, and so on. The current sup- 
plied by the source should be equal to the sum of the amperes 





Fig. 11. Principle of Parallel Distribution. 


required by all of the lamps or other devices that are connected at 
any given time. The voltage should be as nearly constant as pos- 
sible ; hence the system is designated as constant potential, but this 
is only approximately true. In the case illustrated, the dynamo 
generates 112 volts, which is slightly reduced by the resistance of 
the wires until it falls to 110 volts at the last lamp. 

Parallel systems are far more important in electrical distribu- 
tion than series systems; since practically all incandescent lamps, 
a large proportion of arc lamps, and nearly all electric motors, are 
supplied by them. Constant potential circuits are usually more 
complicated than the simple series systems, there being only a 


LANA fis DIGLLMS (OF ELECTRICAL DISTRIBUTION. 29 


single path for the current in the latter case, while with parallel 
connections there are a number of branching paths. Furthermore, 
the maintenance of a uniform voltage over a large district is 
exceedingly difficult. The “drop” or loss of voltage, due to the 
resistance of conductors, which has already been discussed on 
page 9, is particularly objectionable in incandescent lighting, since 
the slightest decrease of potential produces a very considerable 
diminution of light. For example, the candle-power of an ordinary 
lamp is reduced from 16 to 15, which is more than 6 per cent, 
wken the pressure falls from 110 to 109 volts, or less than 1 per 
cent. Such a very small variation in pressure would hardly be 
appreciable in any other practical work, such as steam or gas 
distribution. 

The drop in pressure produces three different effects in the 
lamps or other devices supplied by parallel circuits : — 

(1) All of the lamps receive a lower voltage than that gene- 
rated by the source of electrical energy. 

(2) Some lamps may be supplied with a lower pressure than 
others. | 

(3) The potential at some lamps may vary when others are 
thrown on-or off the same circuit. 

The least harmful of these effects is the first, which merely 
requires the generator to be run at a little higher voltage, and does 
not necessarily involve any difference between the candle-power of 
the lamps, since the drop may be made substantially the same for 
all of them by some of the methods described later, 

On the other hand, varzations in the candle-power of lamps, due 
to either of the last two effects, are extremely objectionable and 
difficult to overcome. In order to study these problems let us take 
a specific case, and assume that 100 incandescent lamps are to be 
supplied with electric current. They are supposed to be divided 
into five groups of 20 lamps each; each lamp requires a current of 
110 volts and. one-half ampere, and gives 16 candle-power ; there- 
fore one group takes 10 amperes, the total current being 50 am- 
peres. The members of each group of lamps are connected in 
parallel in the usual manner, but will be indicated by a single line 
in the following diagrams in order to avoid confusion. These 
groups are assumed to be 200 feet apart in a straight line, making 
a total distance of 800 feet between the extreme groups, as shown 


3 ELECTRICILIGHIING. 


in Fig. 13. The five groups of lamps represented by the light 
vertical lines are connected together by two conductors, which are 
shown as heavy horizontal lines. [hese conductors correspond to 
the so-called szazzs in electrical distribution systems, to which are 
connected the /eads or small branch wires actually supplying the 





Fig. 12. Arrangement of Feeders and Mains. 


lamps. The mains receive their current through feeders, AA and 
LL, which connect them with the generating plant J, as represented 
in Fig. 12. .As a general rule no lamps are connected directly to 
the feeders. The celebrated “Feeder and Main” patent of Edi- 
son * covered this arrangement of electrical conductors. 

In the first case, represented in Fig. 18, the mains are supposed 
to be fed at one end, the feeding-points being represented by short 
vertical lines marked + and — respectively. The mains are as- 
sumed to consist of No. 0000 wire,.A. W. G., which would weigh 
1,025 pounds for 1,600 feet required. Each section of the mains 
consists of 200 feet of No. 0000 wire, and has a resistance of about 


800 ft..No.0000 Se ey 









Current =|10 AMP, 


Drop = "4 VOLTS ; : 
P.D.= 111 VOLTS 110.2 109.6 109.2 (09. 


Fig. 13. Feeding at One End of Mains; 1025 Ibs. Copper; 2 Volts Max. Difference Between 
Lamps; 111 Volts at Feeding-Points ; 1.2 Volts Average Drop. 


.01 ohm. The current in the first section of the + main is 40 
amperes, since it supplies 4 groups of lamps taking 10 amperes 
each, hence the drop is 40 x .01 = .4 volt. Similarly the drops in 
the other three sections are found to be .8 .2 and .1 volts respec- 
tively. The drop in the — main has exactly the same values, but is 
in the opposite direction, the fall of potential being always in the 


* U.S. Patent, No. 264,642, Sept. 19, 1882. 


PARADE Eien hie OF RLECTRICAL DISTRIBUTION. of 


direction in which the current flows. The distribution of potential 
is shown in an exaggerated manner in Fig. 14. It will be seen that 
a potential of 111 volts, supplied at the feeding-points, gives 109 
volts at the other end, therefore no lamp receives a pressure more 
than one volt greater or less than the normal value of 110 volts. 
The horizontal axis OO would represent the line of zero poten- 
tial when the system is uniformly insulated, in which case the 
potentials of the mains at the feeding-points would be + 55.5 volts 
and — 59.5 volts respectively. A defect in the insulation at any 
point would tend to cause the potential of that point to approach 
zero, as already explained in connection with Figs. 4 and 5; and 
if the — feeding-point were grounded, the + feeding-point would 


+ 
Drop= AVolt 






109, 


Drop= 


Fig.\4, 


Fig. 14. Potential Diagram Corresponding to Fig. 73. 


become + 111 volts, all the potentials having positive values. 
ok the potential dzfference would remain the same in all cases. 

| Tapering Conductors. — The use of tapering or “conical ear 
ductors in place of the ordinary cylindrical ones is hardly practica- 
ble, on account of the difficulty of making a wire or rod of that 
form. It is possible, however, to use a jointed conductor com- 
posed of sections of different sizes of wire. The object of such 
an arrangement is to proportion the cross-section of the conductor 
to the current which it has to carry in cases where the current 
varies from point to point, this being the usual condition in parallel 
distribution. If Fig. 13 be modified in such a way that the size 
of each section of the main is proportional to the current passing 
through it, Fig. 15 is obtained. In this case the drop in each 
section will be .25 volts, being the same for all. Hence the po- 
tential falls uniformly from the + feeding-point to the end of the 


b2 ELECTRICVLIGH TING. 


main, and would be represented by a straight line, instead of the 
broken one in Fig. 14. 

It is sometimes stated that the use of tapering mains secures 
economy in copper, but such is not the case in ordinary parallel 
distribution. The weight of copper required in Fig. 15 is 1,013 
lbs., which is practically the same as the 1,025 Ibs. called for in 
Fig. 18. The fallacy arises from the fact that the conductor is 
assumed to be a true cone, the elements of which are straight lines. 
As a matter of fact, the elements would curve outward since the 


i 
cone should be one-half the cross-section, or Vee ofethe 


diameter at a point midway between the base and the apex, in- 
stead of one-half the diameter. 


fxreemesteae 200) Phen = 200" == Bfea toes 200! ee Bigaene B00’ =F 





317 2. No.000 9 SF PS. Nol ie oNo.000.55 8 No.l) oa 
Resis. = .00625 Ohm 0083 0125 025 
Current= 
Current= |]OAmp. 10 
Drop= .25 Volt 
PD.= volts 110.5 HO 109.5 109 





Fig. 15, Tapering Mains; 1,013 Ibs. of Copper; 2 Volts Max. Difference Between Lamps; 
1171 Volts at Feeding-Points; 1 Volt Average Drop. 


Tapering conductors give a uniform drop, as already stated ; 
and the average drop is slightly less than with cylindrical wires, 
being 1.2 ‘volt.in Fig. 48)"and divoltsing ie lo). SE his asenot a) 
matter of great consequence, however, as it is customary to con- 
sider the szaxzmum drop in electrical distribution, and that is the 
same for the two cases when all the lamps are connected. If only 
the first groups of lamps were lighted, the tapering conductors 
would give considerably less drop than cylindrical ones. Never- 
theless, it is doubtful in practice if the advantages are worth the 
extra trouble of laying and connecting several different sizes of 
wire. Where the distances are considerable, and where joints or 
cut-outs would be introduced in any event, it may be desirable to 
vary the size of a main in proportion to the current it is to carry 
at different points. In this discussion it is of course assumed 
that the conductor must always have sufficient current capacity, 
whether it be tapering or cylindrical. 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 88 


In the next case, Fig. 16, the mains are supposed to be fed at 
their centers, as shown. In this arrangement No. 2. wire, weighing 
321.5 lbs., gives almost exactly the same variations of potential 
as in the two preceding cases, the maximum pressure being 111 


Resis. —= .032 OHM 
Current = 10 AMP. 








Current =|10 Amp. 


Drop = 232 VOLTS . 
P.D.= 109.08 voLTs 109.72 : 109,08 


Fig. 16. Feeding at Middle of Mains; 321.5 Ibs. Copper; 1.92 Volts Max. Difference Between 
Lamps; 111 Volts at Feeding-Points; 1.3 Volts Average Drop. 


volts and the minimum 109.08 volts. This shows that a great 
saving of copper is effected by simply feeding the mains in the 
middle rather than at the ends. Theoretically, it would only re- 
quire one-quarter as much copper in the former case. ‘This is 
easily seen, when it is considered that the mains in Fig. 16, on 
each side of the feeding-point, are one-half as long, and carry about 
one-half as much current, as those in Fig. 13, consequently the 
conductor need only have one-quarter of the cross-section to give 
the same drop. The weight is found to be slightly more than 
one-quarter in the example, because the average current is in the 
proportion of 15 to 25 instead of 1 to 2. 

The next case, Fig. 17, represents the mains fed at opposite 
points. This was formerly called the lWerdermann system, after 






SS se SRS pre ara AN mn mr 

Resis. =— ff 205 OHMS os 05 OS 

Current = 40 Amp, 30. 20. 10- 

Drop = 2 VOLTS I 
10/AMP, A 

Current = 10:AMP, 


Drop — .5 VOLTS 
P.D, = 111 VoLTs 109.5 109. 109.5 lik 


Fig. 17. Feeding at Opposite Ends of Mains; 202.2 Ibs. Copper; 2 Volts Max. Difference Between 
Lamps; 116 Volts Between Feeding-Points ; 6 Volts Average Drop. 


its inventor, but is now known as the anti-parallel or return loop 
method of distribution. In this case the same length (1,600 feet) 
of No. 4 wire, weighing only 202.2 lbs., gives an equally good 
distribution of potential. It is sometimes supposed that this ar- 


34 ELECTRIC LIGHTING. 


rangement must give a perfectly uniform pressure at the lamps, 
since the sum of the distances of each lamp from the feeding- 
points measured on the two mains is a constant. As a matter of 
fact, however, the middle lamps will receive a lower voltage than 
those at the ends, as shown in the diagram. This is due to the 
fact that the former are supplied through the portions of the main 
conductors which carry heavy currents, and in which the drop is 
greatest. For example, the drop on the mains in the case of the 
central group of lamps is 


2+15+1.5 + 2 =7T volts, 
but for the end group of lamps it is only 
24+15+4+1-+ 0.5 = 5 volts. 


It is possible, however, to secure a perfectly uniform pressure at 
all points between the mains, if their cross-section is made propor- 
tional to the current in each section by the use of the so-called 
conical conductors already described. In this way the drop in 
each section will be the same, and each group of lamps will receive 
exactly the same pressure, being equal to the difference of poten- 
tial between the feeding-points minus the drop in four sections. 

In the next example the mains are fed at distributed points as 
represented in Fig. 18. In this case No. 7 wire, weighing only 





ee ee ee 
Resis. — +1 OHM zi Al Jl 1 
Current — 10 AMP. 0. 20. 10- 
Drop — 1 VOLT T 
| A 
Current 10 Amp. 10- 
Drop = 1 VOLT 2 3 1 
P.D,— 109 VOLTS 11 TI! wid * “109 


Elec. World 
Fig. 18. Feeding at Distributed Points on Mains; 1017 Ibs. of Copper; 2 Volts Max. Difference 
Between Lamps; 116 Volts Between Feeding-Points; 6 Volts Average Drop. 


101 lbs., gives no greater variation in voltage (i.e. one volt from 
the normal) than No. 0000 wire, weighing 1,025 lbs., in Fig. 18. 
These examples show the great difference that is made by chan- 
ging the points at which the feeders are connected to the mains. 
It should be carefully noted, however, that in both the last 
two cases (Figs. 17 and 18) the feeders must supply 116 volts to 
the mains instead of only 111 volts, as in the preceding examples 


PARALLEL SSL LIIS OF ELECTRICAL DISTRIBUTION. 30D 


(Figs, 18, 15,and 16). In Fig. 17, for instance, the difference of 
potential between the feeding-points + and — must be 116 volts, 
in order that the end group of lamps A shall receive 111 volts, 
since there is a drop of 


2+15+4+1-+40.5 = 5 volts. 


in the upper main. Similar reasoning applies to the group A in 
Fig. 18, the drop being 3 + 2 = 5 volts. This necessity for sup- 
plying a considerably higher voltage at the feeding-points of the 
mains is disadvantageous in two respects. First, it involves a loss 
of power in watts equal to the extra pressure multiplied by the 
total current ; and second, it may allow great variations in poten- 


+ 







200 FT. NO.8. .13 OHM. 
20AMP. 2.6 VOLTS DROP 






~ 111 VOLTS. 









200 FT. NO.8. 13 OHM. 
5 AMP. .65 VOLTS DROP 










109.05 VOLTS 
409.05 


VOLTS 





200 FT. NO.8. 13 OHM, 
15 AMP. 1.95 VOLTS DROP 





200 FT. NO.8. 13 
OHM. 

10 AMP. 1.3 VOLTS 

DROP 







100 FT. NO.8. .065 OHM. 
25AMP. 1.63 VOLTS 








109.7 VOLTS&. 
109.7 VOLTS. ; 


Fig. 19. Closed Ring; 2,000 ft. No. 8; 100 Ibs. Copper; 115.23 Volts Between Feeding- 
Points; 1.95 Volts Max. Difference Between Lamps; 5.58 Volts Average Drop. 


tial to occur when a large number of lamps are thrown on or off 
the circuit. For example, if all the lamps except one were put out, 
the remaining one would receive practically the full pressure of 
116 volts. This may be overcome by reducing the voltage of the 
feeders when lamps are disconnected, either by automatic or hand 
regulation, employing some of the methods described later ; but it 
is evidently simpler to maintain the same pressure at the feeding- 
points. On the other hand, the drop in the feeders themselves 
must be overcome by raising the voltage at the generating plant 
when the current carried by them increases. In such cases it may 
not involve very much additional trouble to regulate for the drop 
in the mains as well as for that in the feeders. 


ead 


36. ELECTRIC TIGHGING. 


A further extension of the principles shown in Figs. 17 and 18 
is indicated in Fig. 19, in which five groups of lamps are connected 
across the mains, which form complete circles, being fed at diamet- 
rically opposite points. In this case, 2,000 feet of No. 8 wire, 
weighing 100 lbs., is used, instead of 1,600 feet, as in the previ- 
ous examples. A similar arrangement is shown in Fig. 20; but 
the lamps are assumed to be divided into four groups, of 25 lamps 
each. All the lamps receive exactly the same voltage, 1,600 feet 
of No. 10 wire, weighing only 50 lbs., being required. This exact 
equality in voltage is due to this being a special case, in which the 
lamps happen to be symmetrically placed with respect to the feed- 
ing-points. In Fig. 17, for example, the second and fourth groups 


200 FT. NO.10..2 OHM. 
4110 VOLTS. 12.5 AMP. 2.5 VOLTS DROP 











110 VOLTS&s 


100 FT. NO. 10. .1 OHM. 


25 AMP. 2.5 VOLTS. 
DROP 






200 FT. NO.10..2 OHM. 
12.5 AMP. 2.5 VOLTS DROP 


100 FT. NO.10. 1 OHM. 
25 AMP. 2.5 VOLTS DROP 


110 VOLTS. 110 VOLTS. 


Fig. 20. Closed Square; 7,600 ft. No. 10; 50.3 lbs. Copper; No Difference Between 
Lamps; 117.5 Volts Between Feeding-Points; 7.5 Volts Average Drop. 


of lamps have exactly the same voltage, since they are equally dis- 
tant from the feeders. The pressure at the feeding-points is 117.5 


_ volts in Fig, 20, being higher than in any of the other cases. 
“Individual Conductors. — The most certain way to obtain a 


constant voltage in parallel distribution is to provide each lamp 


“or group of lamps with its own particular conductors. One arrange- 
. ment of this kind is illustrated in Fig. 21, five groups of lamps, 


: rf each taking 10 amperes and placed 200 feet apart, being assumed, 


~ 


as in the previous examples. The feeding-points, marked + and 


SW —, are supposed to be located at some distance from the lamps, 
\ as shown. The pair of conductors that supply each group are so 
X proportioned in size and length that the drop has an equal value 

) for all of the groups. This condition will be secured if the cross- 


TARA emt LIMO OF LLDECTRICAL DISTRIBUTION. 37 


sections of the various conductors are respectively proportional 
to their lengths. For example, a conductor twice as long as 
another should have double the cross-section, so that the resis- 
tance of the two will be equal. If the currents are not the same 
for the different conductors, the cross-sections should be further 
modified in proportion to the currents. In other words, for all of 


pee 
the pairs of conductors, the fraction “ should have the same value, 
a 


z being the current in amperes, / the total length of both conduc- 
tors, and a the cross-section. 

It is not apparent what advantages this plan of using individual 
wires has over the arrangements already described, the weight of 
copper being even greater than that in Fig. 18, for example. The 


Length = 
Size = 
Resis =]. 





Fig. 21, Individual Conductors; Unequal Lengths; 186 Ibs. Copper; No Difference of Voltage 
Between Lamps; 175 Volts Between Feeding-Points; 5 Volts Drop. 


answer is to be found in the fact that the groups of lamps in 
Fig. 21 are not only equal in potential when all are burning, but 
they are also independent of one another, the turning on or off 
of one or more groups not affecting the others, provided that the 
voltage at the feeding-points + and — be kept constant. In 
the preceding cases, the throwing off of some lamps would vary 
the pressure of all the others. In fact, it was pointed out that 
disconnecting every lamp but one would raise its potential practi- 
cally the whole amount of the drop, which was five or six volts in 
some instances. It was also stated that the remedy for this vari- 
ation consists in regulating the pressure at the feeding-points. 
Thus it appears that it is necessary to maintain a constant voltage 
at the feeding-points, with some arrangements of conductors, and 
a variable voltage with others. These questions will be considered 
later under feeder regulation. 3 


38 RLEGERIC WLC TING 


Fig, 22 represents another example of individual conductors, 
but in this case each group of lamps is supplied through the same 
total length of conductor ; 1.e., 800 feet of No. 8 wire, having 0.5 
ohm resistance. Consequently the drop is five volts for all, since 
each group takes 10 amperes. The advantage of this plan over 
that shown in Fig. 17, which it somewhat resembles, is the free- 
dom from interference already explained. It should be noted, 
however, that in either Fig. 21 or 22 the turning off of a portion 
of the lamps in one particular cluster would affect the remaining 
ones in that group. In order to secure complete independence 
of operation for every lamp in a system, it would be necessary to 
provide each one with its own individual wires. This is practi- 
cally out of the question in almost all cases; but it can be approx- 
imated more or less closely, the tendency in the best practice 
being to subdivide the circuits and reduce the number of lamps 
on each, as far as economy and simplicity will reasonably allow. 


oe ee eee BA aie SETA 


Current =|1O amps. 10 
P.D. at lamps=| 110 volts 110 








Drop=5 volts for each group 


Fig. 22. Individual Conductors; Equal Total Lengths; 200 lbs. Copper; No Difference of Voltage 
Between Lamps; 115 Volts Between Feeding-Points; 5 Volts Drop. 


Calculations of Drop, Weight, etc., of Mains. — The examples 
already given (Figs. 18 to 22) show the results obtained by differ- 
ent arrangements of mains and feeding-points in parallel distribu- 
tion. These cases having been treated concretely with definite 
sizes of wire, voltages, currents, etc., bring out the facts clearly, 
and are intelligible to those who may not possess special mathe- 
matical knowledge. It will be well, however, to discuss these im- 
portant problems in a more general way before dismissing them. 
For this purpose the following symbols may be adopted : — 


L is the length of each main in any desired units ; 

7, the length of each section of main (i.e. between adjacent lamps) ; 

J, and —/,, the currents in the two mains at the feeding-points ; 

z and —z’, the currents in the two mains at the point x; 

V, and v,, the potentials on the two mains at the feeding-points ; 

uy, the potential difference between the two feeding-points, or between 
one feeding-point and the opposite point on the other main ; 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 39 


V’ —v' =u, the potential difference between the two mains at any 
point distant x units from + feeding-point ; 

D, the fall of potential or “drop” at any given lamp with respect to the 
difference of potential between the two feeding-points ; 

C, the current consumed by each lamp ; 

LV, the number of lamps ; 

#, the resistance of each main per unit of length. 


Considering first the ordinary parallel circuit represented in 
Fig. 18, the drop on both mains from the first to the second lamp 
(or group of lamps) is 2 R7C (CV — 1), and the total drop from the 
feeding-points to the last lamp 


D 2 PAO = yeaa a el ae Pn 
In this equation there are V— 1 terms, having an average 
N 
value of So hence we have — 
= RIC (N7— NV), (1) 
and the resistance per unit of length which will give this maximum 
drop D, is — D 


gS 
ZC (WV? — NV) 


(2) 


In the case illustrated in Fig. 16 the current divides, one-half 
flowing in each direction, so that it is only necessary to substitute 
if 
a for JV in the above formule, or 


Des A (wv - 2.N) (3) 


4 D 
2 > ee (4) 
1C(N?— 2) 





and its — 
In the case of anti-parallel distribution (Fig. 17) the drop to 
any lamp, say the zth from the + feeding-point, is R7C [CV — 1) 
+ (N—2)+...-a]onthe + main, and R/C[(V— 1) + WWV—- 2) 
+... (V—-+z-+1)] on the — main. Hence the total drop on 
both mains is the sum of these values which is — 

CEG, 


sy 
od 


D= (N242Nx—83N+42x—22%, (5) 





From this equation it is evident that the drop depends upon ~. 
Differentiating (5), we find that D is a maximum when 
Naat 


©) 
ad 





3 


40 ELECTRIC LIGHTING 


that is, in the middle of the circuit. In fact, this is evident without 
calculation, for the reasons given on page 34. Substituting this 
value in (5), we find that 


Dae a (3.N2—4N +1). (6) 
The drop is a minimum when x = WV or 1, that is, at either end 


of the circuit. Hence substituting in (0), we have — 


Gy io 
LEEK aa ae Ouait (2VG <% V). (7) 


This last equation might have been obtained directly from (1) ; 
for evidently in the anti-parallel system (Fig. 17), the drop at the 
first or last lamp is one-half the drop at the last lamp in the ordi- 
nary parallel circuit (Fig. 13), provided the mains are of the same 
size, 
By subtracting (7) from (6) we obtain the greatest difference 
in pressure between any two lamps in the circuit — 


Pia 





Lage TOs ane aoe Cy —2 NV+ 1); (8) 
(Dee eae 
R —. Max min i 9 
ae hE Gl NEA Ty | ) 


The relative economy of the three systems can now be found. 
The weights of copper required are inversely proportional to the 
resistances ; hence calling A,, A,, and A, respectively the cross- 
sections (in circular mils, for example) of the mains, which will 
produce the same maximum difference in pressure between any 
two lamps, we have from (2), (4), and (9) — 

pip AD ee be teat ia cede 
Ria ee 
=4(N*—N):(M—2N):(NV?-2N+1). 

Hence the simple parallel system (Fig. 13) requires more than 
four times as much copper as when the mains are fed in the middle 
(Fig. 16), but there is very little difference between the latter and 
the anti-parallel method (Fig. 17). This comparison is made on 
the basis of a certain maximum dfference in pressure between any 
two lamps on the circuit. If we consider the same /ofal drop, the 
advantage of the plan illustrated in Fig. 16 is much greater. The 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. Al 


relative weights of copper required by the three systems then be- 
come from (2), (4), and (6) — 


A,:A,:4, =4(N?— N):(N?—2N):(3N?—-4N+1). 


As an example to illustrate the use of the above formula, let 
us assume that twenty 16-candle-power lamps, each taking one-half 
an ampere, are placed ten feet apart on mains each 200 feet long, 
the maximum allowable difference between any two lamps being 
one volt. Hence /= 10, V= 20,C = .5, and D=1. The resis- 
tance per foot by the ordinary parallel arrangement would be 
from (2) — | 1 


Peeper Oe tT, 00053 ob 
1 10 x .5 (400 — 20) Bay 


which corresponds to a No. 7 wire (A. W. G.). 
By the second method (Fig. 16) it would be — 
4 
2 


eh eee ee PN HE 50999. olin: 
; 10 x .5 (400 — 40) 


corresponding to No. 18 wire. And by the anti-parallel system — 


4 


ee 
10 x .6 (400 — 40 4 1) 





== UAV VAL Nis, 


which also corresponds to No. 18 wire. 

By the first two systems, however, the total drop would be but 
one volt, while with the anti-parallel plan, the adzfference between 
the lamps having the highest and lowest pressure would be one 
volt. This is proved by finding the drop to the first lamp,’ from 


10 x .00221 « .5 
2 


Chi wig | L/int (400 — 20) = 2.09 volts, 


and the drop to the middle of the circuit, from (6) — 


LOD KOO: 


= : 71 X 8 (4200 — 80 + 1) = 3.09 volts. 


Hence the greatest difference in pressure is one volt, but the 
total drop to the middle lamp is 3.09 volts for the anti-parallel sys- 
tem. The same size of wire (No. 13) gives a total drop of only 
one volt, if arranged according to Fig. 16 ; and for the simple par- 
allel method (Fig. 13), the maximum drop with No. 138 wire is 
found by (1) to be — 


D=10 X .00221 X .5 (400 — 20) = 4.18 volts. 


49 ELECTRIC WIGHTING: 


In short, for the same maximum difference in voltage in the 
three systems, the relative weights of copper are, roughly, 4:1 :1, 
and the total drop, 1:1 : 3.09 volts; while for the same weights of 
copper, the maximum differences in pressure are 4.18 :1:1 volts, 
and the total drop, 4.18: 1 : 3.09 volts. 

The problems of calculating and comparing the results obtained 
by different arrangements of conductors in parallel distribution be- 
ing of great importance in electrical engineering, it will be well to 
give other general methods of solving them. These are largely 
derived from Abbott’s work on Electric Transmission of Energy, 
with certain modifications and corrections. Let it be supposed 
that the mains supply an indefinite number of lamps or other 
devices uniformly distributed along their entire length. This is 
equivalent to assuming that the current supplied by the generating 
plant flows between the two mains in a uniform sheet throughout 
their entire length. 

CasE I. Cylindrical Conductors. Parallel System. — Fig. 23 
represents two parallel cylindrical conductors connected to the 
source of supply at 4 and C. From each element, dr, of the + 
main AS, along its entire length, an elementary amount of current 
will pass to the other main, CD. Hence the current decreases 
uniformly from its maximum value /,, at the point A, to 0 at the 
point 4. At any point x, the current in the mains will be the total 
current /,, minus all the current which has flowed across from one 
conductor to the other, between the point A and the point x under 
consideration. This latter quantity will be 4, / Z, since the flow 
of current per unit of length is /,/ Z. 

By Ohm’s law the variation in potential in any conductor is 
fiz Ri, Uhe resistance “of theyelement(727for both ainaincees 
2 Rdx ; hence the drop in pressure for the element dr is given by 
the expression : — 


d (ty — W) = 2 Rdx(Z,— 2%) 2 R11 — 2) ax, (10) 


Integrating between + = 0 and x = L — 





ty — Ww =2R1f (1-2 )dx = 22X72): (11) 


This equation, which gives the drop on both mains between 
the feeding-points 4 and C and any point x, represents a branch 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 438 


of a parabola, to which the conductor may be considered as an 
asymptote. When +=0, u — uv = 0, showing no drop at AC 
which is evident; when += LZ, u — uw’ = RIL, being obviously 
the maximum value of the drop, its average value being 3 RL, L. 
Asvan example, letrit be assumed that — 


i.) Jat peres: V,— v, = 40. 
I, = 60 feet. 02 12x 

nae ee (120 — x), 
he .02 ohm per toot, - ‘ 60 ( 5) 


If x be successively taken as 10, 20, 30, 40, 50, and 60, the 
corresponding values for the drop are 4.4, 8.0, 10.8, 12.8, 14.0, 
and 14.4 volts, from which the curve ZF in Fig. 23 is plotted. 
The curves in Figs, 24, 25, and 26 are also plotted from the same 


m 
Th 

G 
/ 


a Keane K once 
Agile Lower AY? Dee Ata igs me a B 
Vo Vo 
& -I, Y -lo oe ale Pee 
se) ’ 0 ; v! D 
Kee + Leet Kitnmmnennats | sctmnanre 
| 

Fig. 23. Fig. 24. 


Figs. 23 and 24, Parallel Distribution. Cases !. and II, 


data. An inspection of this curve indicates an unequal drop along 
the conductors, evidently due to varying current density in‘ the 
mains. To avoid this variation it is possible to employ tapering, 
or so-called “conical,” conductors, already referred to on page 31. 

CasE II. Tapering Conductors. Parallel System.—In Fig. 
24, AB and CD are two parallel tapering conductors, supplied with 
current at A and C, and having a cross-section which is proportional 
to the current at any point, so that the current density will be 
constant. The same notation as in Case I. will be used, except 
that R, is the resistance of each main per unit of length at A or 
C, the resistance per unit of length at any other point, x, being 
represented by 7 which is evidently a variable. The drop or vari- 
ation in potential for any element now becomes — 





Cm = Oda (7, 3 12). (12) 


44 HLEOCTRICILLGH Live, 


But 7 =p/S at any point, p being the specific resistance and S$ 
the cross-section of the conductor at that point; hence — 


2pJ,(1 —— 2) as 


“ ; 
d (uy —u’) = ao ly, — 12) = G (13) 
But the current density which, by hypothesis, is constant, is — 
See 
eee 
S 
Hence by integrating (13), we have — 

Uo Ué = 2K, 1,x: (14) 


This is the equation of a straight line, indicating a uniform 
drop from AC to BD; uw — uw being a maximum when x = Z, and 
having a value 2 R,/,Z, which is twice as great as in Case I. 
This demonstrates that, with a tapering conductor having the 
same resistance per unit of length at the supply point as a cylin- 
drical one, there is twice’ the drop. if 1s also-a viact thatacne 
weight of copper is one-half as much for the former ; since it is 
not a true cone, the diameter at the middle section being .707 in- 
stead of half that at the base, as already explained on page 32. 
Such a conductor might also be considered as a wedge, two of the 
sides of which are parallel. 

Consequently, with the same weight of copper, there is no 
reduction in the maxzzmum drop when so-called conical conductors 
are employed, as has been claimed. There is, however, a saving 
in the average drop, which is readily seen by comparing the curves 
EF and GH in Figs. 28 and 24, or by substituting 4 Z for x in 


11) and (14), which give BALL as the drop at the middle point 
( g p p 


of the/mains im Case’ [and sel in Case II. The latter value 


assumes that the area of the base of the tapering mains is made 
twice as large as for the cylindrical ones, in order that the weight 
of copper shall be the same for both. Hence the drop at the 
middle point is % as great in Case II. as in Case I., the maximum 
drop being the same, and the average drop being ? as much. 
The loss of energy corresponds to the average drop, hence it is 
also $ as great for the tapering conductors. Usually, however, the 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 45 


maximum drop is the controlling consideration in designing elec- 
trical conductors, particularly for electric lighting. 

Case III. Cylindrical Conductors. Anti-Parallel System. — 
In this case the mains are fed from opposite ends as already de- 
scribed in connection with Fig. 17. It is evident that this arrange- 
ment differs from the two preceding in the fact that no lamp 
receives the full voltage delivered to the mains, because % is at 
one end of one main, and vz, is at the opposite end of the other. 








i K M N 
URNS eco he---- ee 
\se 
= 
L. fs al. es 
yet san 


Figs. 25 and 26. Anti-Parallel Distribution. Cases Ill. and IV. 


A study of Fig. 25 shows that the variation in pressure between 
the ends of any element dr for both mains is equal to the aiffer- 
ence between the drop in one main and that in the other, whereas 
in the two previous cases it was the sam of the two drops, hence — 


a(t, — uw’) = Rdx(t—2'), (15) 


tz and —z' being the currents in the respective mains at the point 


Ld 


x, and having the following values : — 





eae fem La and, ae See Ly 
ye vs 
substituting these in (15), we have — 
Des . 
a (Up th ome Le L, (1 — =) dX (16) 


Integrating — 
Uy — Wy = fea Ay [ 


This equation is also that of a parabola, but its axis is perpen- 
dicular to the mains at their middle point. When zx =0orr= lL, 
ut — u' = 0, showing that at each end the lamps receive the same 
voltage. To locate the maximum difference in pressure between 








=*) pp Sg aeey a alg 


L 


the lamps —- 


46 ELECTRIC LIGHTING. 


sgt) man (ta an 2eherao 
aX 


(18) 


that is, the greatest drop is at the center of the mains, and has 
the value R/,L /4 obtained by substituting (18) in (17). But it 
should be carefully noted that this represents the dzfference be- 
tween the voltage of the middle lamp and that of either end lamp. 
For the latter the pressure is less than the difference of potential 
between the feeding-points (= V, — uv) by the quantity RAL / 2, 
which is the total drop in either one of the mains. Hence the 
middle lamp receives a voltage which is less than that supplied to 
the feeding-points by an amount — 


Kel a L aah Lo en ee 
0 Ores on" 19 
4 a Zz 4 OH 








This value is only three-quarters as large as the maximum drop 
in Case I., which was found to be A/,LZ, and the greatest aiffer- 
ence petween the voltage of lamps is only one-quarter as much, or 
RIpL / 4, the weight of copper being the same. 

Case IV. Tapering Conductors. Anti-Parallel System. — 
The plan of feeding from the opposite ends of the mains may be 
applied to tapering conductors with even greater advantage than 
in the case of cylindrical conductors. By applying the equations 
in Cases II. and III. to this arrangement, shown in Fig. 26, the 
following expression is obtained : — 


a (Uy — Wy) = (r2 — 2’) ax. 


vy and 7’, as well as z and —z’, being respectively the resistances 
and currents in the two mains at the point x Hence by a train 
of reasoning similar to that in the previous cases, 7 = p/S, and 
r' = p/ S'; but pz/ S and pz’ / S' are constants for each main, by 
hypothesis, and are equal to each other, hence — 


qo #) 9, (20) 


Dax 
“Uy — w' =a constant, and 
LVS ge mae] eT (21) 
In other words, there is no difference in the voltage supplied 
to the various lamps, the pressure at any lamp being the difference 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. Af 


in potential between the feeding-points less the quantity R,/,Z, 
which latter is therefore the maximum drop for all of the lamps. 
This is the same value as in Case I., but the amount of copper is 
only one-half as great; hence the maximum drop is one-half as 
much for the same weight of copper, and all lamps receive the 
same voltage. 

Drop in Voltage with Irregular Distribution of Lamps. — In 
the various cases heretofore considered (Figs. 13 to 26 inclusive), 
the lamps were assumed to be uniformly distributed on the mains. 
_This represents not only ideal conditions, but also applies fairly 
well to actual practice at full load; that is, when the maximum 
number of lamps are lighted. In fact, the circuits should be care- 
fully designed to approximate this condition as closely as practica- 
ble in most cases. When only a fraction of the lamps are turned 
on, it is evident that they may be very irregularly distributed. 
This would give rise to an almost infinite number of special prob- 
lems corresponding to the possible arrangements that might be 
made ; but there are certain general facts that apply to such cases. 

If in Fig. 13 it be assumed that only the last or right-hand 
group of lamps is connected, the drop would be equal to the cur- 
rent multiplied by the total resistance of both mains, or 10 x .08 
= .8 volt. Hence the potential difference supplied to this group 
of lamps would be the pressure at the feeding-points minus the 
drop, that is, 111 — .8 =110.2 volts. If now the middle group of 
lamps be turned on also, the potential difference which they re- 
ceive would be 111 — 20 x .04 = 110.2 volts, and the pressure at 
the last group becomes 111 — (20 x .04 + 10 x .04) = 109.8 
volts. Thus the various groups may be lighted successively, and 
it will be found that — 


1. The addition of each group reduces the pressure for all of 
those already connected. 

2. The maximum drop occurs when all of the lamps are con- 
nected. | 

3. The greatest difference between the voltage of any two 
lamps will usually exist when all are turned on. 


The first statement might be contradicted on the ground that 
the pressure at the first group of lamps connected directly to the 
feeding-points would remain the same whether the others were 


48 FLECLTRACCLIGLHZ ING. 


lighted or not. ‘Theoretically this is true; but practically there 
would be some drop on the mains even for this group, unless it’ 
were connected exactly at the feeding-points ; and there would 
always be a drop on the feeders when any lamps were turned on, 
unless it is overcome by some of the special methods of feeder 
regulation which will be described later. 

The same statements apply to Fig. 16, in which the portions 
of the mains on each side of the feeding-points may be considered 
as corresponding to the whole mains in Fig. 18. Even though all 
the lamps on one side were connected, and only one on the other 
side, the total drop and the difference between the voltage of lamps 
would be no greater than for the full-load conditions represented 
in the diagram. 

Similar reasoning is applicable to the arrangements shown in 
Figs. 17 and 18; in fact, any two groups of lamps would have the 
same pressure in the case of the former, and any number less 
than all would give no greater total or difference in drop than the 
full load of lamps. If the first three groups were lighted, and 
only a single lamp out of the last group was turned on, the latter 
might receive a potential about three volts higher than that of the 
others. This is greater than the maximum difference when the cir- 
cuit is fully loaded, which is only two volts. Hence it appears that 
when one end of a pair of anti-parallel mains is heavily loaded, and 
there are very few lamps in circuit at the other end, the difference 
between the voltage of lamps at the two ends is greater than when 
the full load is turned on. Consequently this is an exception to 
statement 3 above. But even in this case, the maximum drop and 
the average drop are less with a fractional load. 

In Fig. 27 the curves AB and CD represent the potentials on 
two cylindrical mains, which are fed according to the anti-parallel 
method at 4 and D respectively, being fully and uniformly loaded. 
The drop between A and £ is greater than between C and //, 
because the average value of the current is greater for the former, 
as will be seen by comparing Fig, l{- “Hence the pressure sup- 
plied to the middle lamps #7 is less than that at the end lamps 
AC, as already explained in connection with Figs. 17 and 25. If 
now ail the lamps on the right-hand half of the mains be discon- - 
nected, there will be no drop between & and /, and the fall of poten- 
tial from HY to D will be constant, and will be represented by the 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 49 


straight line HD. It is evident from an inspection of this diagram 
that (D — EH > BD — LY, or in other words, there is a greater 
aifference between the voltage at #D and EH when half the lamps 
are thrown off. Hence anti-parallel mains, when very- unequally 
loaded, may show an exception to statement 3 (page 47) as already 
explained. It is also apparent, however, that the maximum as well 
as average drop are smaller with any load less than the full amount. 
The substitution of tapering mains for cylindrical ones makes 
the pressure still more uniform for fractional loads, since the drop 
is more nearly equal for the different portions of the conductors. 
When lamps are irregularly connected to a closed loop or ring 
arrangement of mains, the problem becomes somewhat more difh- 


Ant 






, 
Fig. 27. Effect of Unequal Distribution of Lamps on Anti-Parallel System. 


cult, since there are two paths for the current.* Such acase is rep- 
resented in Fig. 28, in which a pair of ring mains are supplied at 
the feeding-points, with a voltage V, the total value of the current 
being /, The resistance of a semicircular portion of each main is 
R. Two equal lamps are assumed to be connected as shown, the 
current in each being $7 Let x be the current that flows down- 
ward from the + feeding-point, then the current in the upper half 
of mains is J — x, and their combined resistance is 2 2, hence, — 


ON (Tc) ot RI— =>“? = Re, (22) 
ani Ome, (23) 
also Mi —Ve= R(w—P)or i + Af = Re (24) 


* This matter will be discussed further under the head of ‘* Networks ’’ of conduc: 
tors. 


50 ELECTRIC LIGHLING. 


From (23) and (24), 


Vy —-W=ni-ht+ ee. (25) 
From (22) and (23), 
ANE 
Y -W= RI (26) 
From (20), 
rere 
GR ACMAN Kg tag (27) 
Substituting this value of V, in (26), 
V Bobet ee § 
V —-V,=R/J—-—+7),-—-—+—- 
1 : 5 eal 9 +- 1 (28) 
Simplifying, we have, 
ys a (29) 
From (27) and (29), 
v= V— S42. (30) 
From (23), 
wb Ail 


R (31) 


To take a specific case, let us assume V7 = 110 volts, 7= 8 
amperes, and K=1ohm. Then we find from (29), (380), and 


rs (I~ x) =3 
Fe 


BR(x- ty ys 





Fig.29. 
Figs. 28 and 29. Irregular Distribution of Lamps on Ring Circuit. 





(31) that Y, =105 volts, Y,= 104 volts, x =5 amperes, the 
current that flows upward from the + feeding-point is 8 —5 = 
3 amperes, the current in each lamp being 4 amperes. Fig. 29 
represents the distribution of potential in this case, including the 


MARA ae Bl Le LAI CAL DISTRIBUTION. ol 


drop in each portion of the mains. The addition of more lamps 
to this circuit, whether symmetrically or unsymmetrically placed, 
would increase the total and average drop, also the maximum dif- 
ference in voltage between lamps. 

The general conclusion is, that the three statements made on 
page 47 apply not only to the simple arrangement shown in Fig. 
13, but also to almost any parallel system of mains, with the 
exception of peculiar conditions on an anti-parallel circuit, as ex- 
plained in connection with Fig. 27. Hence it is ordinarily suffi- 
cient in practice to calculate the distribution of potential on a 
parallel system for full load, since the total or average drop, and the 
greatest difference in voltage between lamps, will almost always 
be smaller for any number or arrangement of lamps less than the 
maximum load. MHeretofore the principal point that has been con- 
sidered in discussing parallel systems has been the difference 
between the pressures supplied to the various lamps which are 
burning at the same tzme. But it has already been explained on 
page 85 that in cases where the total drop is considerable, — 10 
per cent, for example, — the voltage at the lamps will rise nearly 
that same percentage when the full load is thrown off, leaving only 
a few lamps. It will now be well to study the means employed 
to prevent variations in the voltage of a given lamp when others 
are thrown on or off the same circuit. 

—Regulation of Voltage Supplied to Parallel Systems. — The 
pe -points in the various diagrams (Figs. 13 to 29) might in 
some cases be supplied with current directly from the generator, 
or the feeders may be so short that their resistance is insignificant. 
Under those circumstances it would only be necessary for the dy- 
namo or other source to generate a constant pressure in order to 
supply the mains represented in Figs, 13, 15, and 16. If this 
were kept at 111 volts, the last group of lamps would receive’ 109 
volts at full load, and no lamp could receive more than 111 volts, 
even if all but one were turned out, so that the extreme variation 
would be but one volt from the normal pressure of 110 volts. The 
large amount of copper used in these cases saves the trouble of 
regulation, and often might be worth the extra first cost. 

This is practically the way that the majority of isolated plants 
are operated, the size of the wires being made sufficient to limit 
the drop to a small amount so that the dynamos may be run at a 


52 ELECTRIC LIGHTING. 


fixed voltage. With wiring designed for a total drop of 4 per cent, 
the greatest variation from the average pressure would only be 
about 2 volts, and usually the maximum drop is between 2 and 
4 per cent for isolated plants where the distances are moderate. 
In most cases, even the simplest, feeders are employed to connect 
the mains with the generators, so that the pressure lost in them 
must be included in determining the total drop. When the dis- 
tances are greater, or it is attempted to save copper by using 
smaller conductors or by adopting such arrangements of mains as 
those represented in Figs. 17 to 22, the drop becomes too large to 
warrant the maintaining of a constant potential at the dynamo. 
Nevertheless, many small central stations and isolated generating 
plants are operated at an approximately fixed voltage, in spite of the 
fact that the drop may be 5 per cent or more. The usual practice 
in such cases is to run the dynamos about 2 per cent above the 
normal voltage of the lamps, the consequence being that at full 
load the latter receive about 3 per cent less pressure than that for 
which they are intended, assuming the drop to be 5 percent. This 
custom arises from the fear of shortening the life of incandescent 
lamps by feeding them with too high a voltage. 

It appears to be a generally accepted idea that the rated pres- 
sure of a lamp is a /z#22¢ above which it should never be allowed to 
rise. Asa matter of fact, the voltage marked on the lamp should 
be considered as an average value, to be approximated as closely as 
possible at all times. It is a rare thing to see incandescent lamps 
burning even one or two per cent above their rated pressure, while 
they are very often operated considerably below this point. The 
author has observed in thousands of cases in America and Europe 
that incandescent lamps are usually run perceptibly below their 
proper voltage, and at least half of them are so low that they are 
positively dim. This is partly due to the usual falling off in the 
candle-power of lamps which occurs after they have burned for 
some time, amounting to a considerable loss after a run of 500 
hours. This matter will be treated fully under the head of incan- 
descent lamps. In isolated plants, and in many central stations 
where lamp renewals are paid for by the user, this diminution in 
candle-power is great because of the tendency to unduly prolong 
the life of the lamps. But in stations or plants where it is desired 
to render good service, the lamps are renewed more frequently. 


PARALLEL SVSTEMS OF ELECTRICAL: DISTRIBUTION. 583 


The reason for generating a constant potential is the simplicity 
and convenience secured by so doing. The attendant merely has 
to keep the index of the volt meter at a certain point, by means 
of the ordinary rheostat in the shunt field circuit, being either in- 
structed to do so, or naturally falling into that habit. It would 
greatly improve the service, however, if the pressure were kept at 
a given value for any number of amperes up to half load, and raised 
a certain percentage when the current exceeds that amount. For 
example, below half load the dynamo could be regulated to generate 
2 volts higher potential than the normal voltage of lamps, which 
would again be increased 2 volts when the current is greater than 
half load, the total drop being 5 volts. In this way the pressure 
at the lamps would not be more than one or two volts high or low 
at any time, and the extra trouble or intelligence required would 
certainly be insignificant. Indeed, it would seem to be perfectly 
practicable to carry this plan further, and subdivide the load into 
three or even four parts instead of two. The instructions could 
be just as definite and almost as easily carried out as for one fixed 
potential. If this regulation were effected by hand, using the 
ordinary rheostat in the field circuit, it would be a rough approxi- 
mation to the rise in voltage with increasing load which occurs 
automatically in an “over-cox:pound” dynamo 

Regulation by Means of Compound or Over-Compound Dynamos. 
— It would seem that an excellent way to operate systems in 
which a constant potential is required at the lamps or other re- 
ceivers, is to employ generators which are over-compound wound 
to give a rise in voltage from no load to full load the same in 
amount as the total drop, thus automatically securing the desired 
Tesulte een objection to this plan is the tendency for the £47 F. 
of the dynamo to rise, and a very excessive current to flow in case 
of a short-circuit. The 4.47.F. of a plain shunt machine, on the 
other hand, tends to fall with a short-circuit. But when properly 
protected by fuses or circuit-breakers this difficulty is not likely to 
be serious. Another difficulty that may arise in such a case is the 
fact that when there are two or more over-compound generators 
the pressure may be too high when only one is in use. For exam- 
ple, when one machine out of two is running with one-half of the 
total load, it will raise the voltage just as much as if both were 
working at full load, whereas it should only increase the pressure 


54 ELECTRICALIGHTING. 


one-half of the maximum percentage of drop. This trouble may 
be avoided by always leaving in circuit the series coils of all the 
dynamos, or preferably by substituting an equivalent resistance 
for them when they are disconnected.* 

The manner of connecting two or more compound dynamos to 
operate in parallel is represented in Fig. 30. 4 is the armature, 
B the series, and C the shunt field coils, X the field rheostat, D, /, 
are switches connecting the main terminals of the dynamo with 
the ‘bus bars G and / respectively, and & is a switch to connect 


R 





)  Q ( F 
OO 00-0 070 Os 







000009000C 


Fig. 30. Compound Dynamos in Parallel. 


the equalizer f // with the brush from which the series coil B leads. 
It is a common practice to mechanically join D, £, and F bya 
cross-bar so that they move together and form a three-pole switch. 
In such cases, when a dynamo is about to be connected to the cir- 
cuit, the switches D, /, and F are left open, and the field magnet 
is excited by the shunt coil C, being regulated by the rheostat R 
until the pressure generated is a little greater (about one per 
cent) than the difference of potential between the ‘bus bars G and 
f. This fact may be ascertained by comparing two volt meters 


* This matter is explained in vol. i., p. 349. t Vol. i., p. 348. 


PARALLEL aI oLEMS OF ELACTRICAL DISTRIBUTION. 50 


respectively connected to the dynamo and to the ’bus bars, or by 
connecting a single volt meter first to one and then to the other, 
which avoids the error due to a difference between two instru- 
ments. A still better plan is to connect the dynamo to the bus 
bars through a high resistance and a galvanometer which deflects 
one way or the other according to whether the dynamo voltage is 
higher or lower than that of the circuit. For this purpose it is 
very convenient to use a volt meter having a scale on both sides of 
the zero point. After the pressure of the dynamo has been prop- 
erly regulated, the three switches, D, £, and /, are closed. When 
this is done simultaneously with a three-pole switch, a considerable 
current will flow through the series coil 2, which tends to still 
further increase the voltage of this dynamo, at the same time tak- 
ing current away from the series coils of the other machines, and 
thereby reducing their potential. The shifting of load thus pro- 
duced may be so sudden and so great as to be objectionable. To 
avoid this difficulty the two switches & and / are sometimes com- 
bined to form a double-pole switch, the other one, D, being operated 
independently. With this arrangement the double-pole switch 
EF is closed first, allowing the current to flow through the series 
coil 4, and the regulation of voltage is made under these condi- 
tions. The switch JD is then closed, and the -.4/7F. of that ma- 
chine will not change materially. The current which it generates 
will also be small, provided its voltage was adjusted to be only 
slightly greater than that of the ’bus bars. 

When the three switches, D, /, /, are simultaneously closed, 
it is found in practice that armature reaction, etc., tend to lower 
the potential of the generator about as much as the current in the 
series coil tends to raise it, hence the effects counteract each other. 
But it is merely an accident if such is the case, and it can only be 
determined by trial. It often happens that the two actions do not 
balance each other, the rise of 4.4/./. being greater than the fall. 
In these cases, which are common in electric railway stations, the 
attendants learn by experience that the pressure of a dynamo 
should be regulated a certain number of volts below that of the 
*bus bars before it is connected to them, in order that it shall act 
properly when the three-pole switch is closed. This is certainly 
a crude method of working, and increases the chance of having a 
back current flow through the series coil, which would tend to 


56 ET ECTRICLICHLING 


demagnetize the field if the E.7F. of the dynamo is considerably 
less than the pressure at the ‘bus bars, particularly when the 
equalizer is somewhat long or is too small in cross section. 

It would seem to be generally desirable to separate the switch 
PD in order to have independent control of the equalizer. Another 
advantage secured by this arrangement is the field excitation 
that is positively produced when the switch £ F is closed, avoid- 
ing the delay and uncertainty which are always involved when self- 
excitation alone is depended upon. In fact, self-exciting dynamos 
often fail to generate, or become reversed in polarity.* The use 
of separate switches also enables the series coil to be left in cir- 
cuit when a dynamo is not working, for the reasons explained on 
page 58. The three switches D, &, and / might. all be made 
independent ; but there would then be a chance for D and # to be 
closed, and the equalizer switch & left open, which is likely to 
cause serious trouble, due to an excessive or reversed current in 
the series coil £; or the switches D and & might happen to be 
closed with / open, in which event the series coil would not be in 
circuit, and the dynamo could not generate sufficient voltage when 
the load increased. 

Compound or over-compound generators are generally used in 
isolated plants and smaller central stations, and are almost uni- 
versally employed in electric railway power-houses; but in large 
electric-lighting stations plain shunt dynamos are often employed 
in order to give greater flexibility of regulation. In such systems 
the lamps and other devices. are supplied through a number of 
feeders, which are fed with different pressures at the station 
according to their length and the load upon them. The methods 
employed will be described later under the head of “ Feeder 
Regulation.” It should also be noted in this connection that the 
business of large stations warrants the constant employment of 
one or more men to regulate the voltage, while in small plants 
the regulation should be automatic as far as possible, in order to 
reduce the required attendance toa mimimum.. It is not unusual 
for such plants to be left to take care of themselves for consider- 
able periods of time. In most cases automatic regulation has to 
be supplemented more or less by hand adjustment of the field 
rheostat to make up for change in speed due to variations in 


* Vol. i, p. 362. 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. O51 


steam pressure or water pressure in the case of hydraulic power. 
The heating of the field coils and resistances in shunt and com- 
pound dynamos, as well as hysteresis in the magnets, also cause 
variations in the voltage which usually have to be overcome by 
hand regulation. { 


Automatic Constant-Potential Regulators. — To entirely avoid 
the necessity for hand regulation, or to reduce it to a minimum, 

























































































Filganate 
Belknap-Chapman Automatic Voltage Regulator. 











automatic devices may be used to maintain constant potential. 
One of these regulators, illustrated in Fig. 81,* consists essentially 
of a rheostat in the shunt field circuit, whose moving arm, J, 
is operated by a solenoid, Q. A relay solenoid, A, is connected 
across the main conductors through the binding-posts f 7’, and 
has contact points, z, that govern the admission of current to the 
working solenoid Q. The latter is differentially wound with four 
coils, two of which have a small continuous current flowing through 
them, and are in opposition to each other, the current being sup- 


* Electrical World, N.Y., March 20, 1897, p. 395. 


58 FLECTRICOIIGHTING 


plied through the switch G, and binding-posts £28. The other 
two coils, when the circuit through them is closed by the relay, 
act to neutralize one of the continuously excited coils. This method 
of operation avoids the injurious sparking that would occur if the 
circuit of the main solenoid were actually broken, and thus per- 
mits a close adjustment of the relay contact points, and secures a 
more sensitive regulation. The cores of the solenoid are composed 
of small, soft iron wires to give quick action and reduce hysteresis 
effects. Two lamps, / F", constitute a non-inductive resistance for 
the relay circuit. An ordinary hand rheostat, £, is included in 
the shunt field circuit in order to adjust the resistance, and also 
give independent control. The voltage for which the device is set 
may be altered by shifting the small weight / on the relay lever. 
In this device the consumption of energy is not large, being only 
60 or 70 watts for a large regulator. The construction as de- 
scribed would tend to maintain a constant potential at the points 
on the circuit to which the binding-posts 7 f' are connected. It 
is evident that these may be in the station or at any desired posi- 
tion on the system of conductors, thus producing the effect of over- 
compound winding. This would necessitate the running of special 
pressure wires to some distance, which may be avoided by provid- 
ing the relay solenoid, A, with a series coil in addition to the shunt 
coil, or, in short, by compounding the regulator instead of the field 
magnets themselves. The series coil would have to be connected 
in the main circuit, or shunted around a resistance placed in it. 

In order to maintain a constant current for charging storage 

batteries and for other purposes, the relay 4 is wound with a series 
coil only. These devices are also made for alternating current 
regulation. <A later form of the Chapman regulator is described 
in the Electrical World, April 16, 1898, p. 480. 
— Methods of Exciting the Shunt Coils of Dynamos. — The three 
principal ways of exciting the shunt field coils of either a plain 
shunt or compound generator are known as Self excitation, ’Bus 
excitation, and Separate excitation. 

If self-excited, the terminals of the shunt field coils are connected 
to the brushes, hence the magnetism gradually dies away as the 
dynamo is slowed down after being disconnected from the circuit ; 
and when it stops the field has disappeared, except a little residual 
magnetism. This avoids the danger of piercing the insulation of 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 59 


the field or armature winding, which is likely to occur if the mag- 
netism be suddenly discharged. The disadvantages of this method 
are the slowness with which the dynamo builds up its own field, 
and the possibility that it may entirely fail to generate, or become 
reversed in polarity. In ’bus excitation the shunt field coils are 
fed from the station mains or ’bus bars, the advantages being the 
fact that the field magnetism is promptly and positively brought 
to full strength so that the dynamo may be connected to the others 
as soon as it attains its speed, and the polarity cannot become 
reversed. On the other hand, the field may be accidentally left in 
circuit after the dynamo is stopped, and it is always necessary to 
discharge it through a bank of lamps or other resistance by means 
of a field break switch. This method of discharge, although safe, 
might cause trouble if the bank of lamps were disconnected, or 
otherwise out of order. 

With separate excitation the field circuits of the generators 
are connected to a special dynamo or other source of current. 
This plan has all the advantages and disadvantages of ’bus excita- 
tion, and has the additional merit that the field strength is not 
_ affected by changes in voltage occurring on the main circuit, which 
would tend to aggravate the variations. It also has the difficulty 
that the exciting dynamo or battery is comparatively small, and 
may therefore be weak and unreliable. An accident to it would 
incapacitate as many generators as were being charged by it. In 
a three-wire system the shunt field circuits of the dynamos on one 
side may be supplied with current from the other side of the sys- 
tem, which practically amounts to separate excitation, except that 
an extra generator is not required. But if any trouble occurs on 
one side it is likely to affect both sides of the system. 

In the method of excitation devised by Mr. W. I. Donshea,* 
and represented in Fig. 82, one terminal of the shunt field winding 
S leads to one of the brushes C, while the other end is brought 
through the regulating rheostat # to the blade of the field switch 
/. This blade is pivoted on the same axis as the main dynamo 
switch 7, but the two are not electrically connected together. 
The other main switch, /V, and field switch, / are first closed, J7 
being left open. This completes the field circuit so that it is 
excited from the ’bus bars 8 + and B— as shown. When the 

* Electrical Engineer, N.Y., Jan. 22, 1896. 


60 ELECTRICULIGHIING. 


dynamo is regulated to the proper voltage, the main switch J7/ is 
then closed. On the blade of the latter there is a catch which 
engages with the blade of the field switch / and locks them to- 
gether, also forming an electrical contact. When the main switch 
M is opened in order to throw the machine 
out of circuit, it brings the blade of the field 
switch with it, the two remaining in elec- 
trical connection ; the field being now self- 
excited dies away gradually as the dynamo 
slows down. The switch VV may then be 
opened in order to entirely disconnect the 
machine from the circuit. When the dy- 
namo is required again, the catch that locks 
the two switches together is withdrawn, and 
the field switch is closed independently, the 
other steps having already been described. 
This method combines the advantages of 
self and "bus excitation without involving 
complication. The ’bus bars & + and B — 
in Fig. 82 may be indefinitely extended in 
either direction; and any number of dyna- 





mos may feed current to them, the connec- 
tions and operation being the same for each. 
If there happened to be no current on the 
‘bus bars, owing to accident or the stopping of all the machines, 
any one of them could be started as a self-exciting dynamo by 
closing the switches / and MM. 


Fig. 32. Donshea Method of 
Shunt Field Excitation. 


The excitation of a compound generator is conveniently and 
effectively accomplished by causing current from the other ma- 
chines to flow through its series coil; for example, the switches. 
F and F in Fig. 30 are first closed, as already explained. But a. 
compound dynamo working alone would have to build up its own 
magnetism the same as a series or shunt machine. In the case of 
the last named, it excites more readily the higher the resistance in 
the external circuit, hence the latter should be opened if possible. 
But with a series or compound the excitation is facilitated by short- 
circuiting the main terminals so that a strong current will flow in 
the series field coils. This should be tried, however, only when 
the machine refuses to generate under normal conditions ; and the 


PARALLEL wae OLN DLE CARICA LIS LAL OT TION, 61 


short-circuit should be carefully applied for brief periods, otherwise 
a very excessive current may be produced. The causes and reme- 
dies for a dynamo failing to generate are given in Vol. I., p. 862, 
-and more fully in Practical Management of Dynamos and Motors 
“by Crocker and Wheeler, p. 155. 

Feeder Regulation. — It has been stated on page 51 that the 
ordinary practice in the smaller electric-lighting plants is to oper- 
ate the generators at a fixed voltage, or to supply a somewhat 
higher voltage as the load in amperes increases, in order to make 
up for the drop in pressure on the conductors, The rise in vol- 
tage is produced by hand regulation, over-compound winding, or by 
an automatic regulator, as already described. In large systems of 
distribution the various feeders (Fig. 12) may differ greatly in 
length, and may be very unequally loaded, the latter condition being 
in a continual state of change. It therefore becomes necessary to 
independently control the different feeders, for which purpose sev- 
eral methods are employed, as follows :— 

1. Connecting and disconnecting feeders at various points on 
the mains; 2. Peeder rheostats; 3. Auxiliary “bus bars; and 4. 
« Boosters.” | 

The first of these methods is represented in Fig. 38, in which 
a pair of mains, P Q and X& S, are supphed with current from the 


E A 





Fig. 33. Feeder Regulation by Disconnecting Feeders. 


generator D by means of feeders A, B, and C, the corresponding 
return feeders being shown below. It is assumed that there are 
considerably more lamps burning at _/ and Z than at A, hence the 
voltage would be higher at A than at / and JZ, if all three feeders 
were in circuit. This difference will be reduced by opening the 
switch /; thereby disconnecting the feeder #4, as indicated. The 


a 


62, ELECTRICOLIGHTING 


small amount of current required for the few lamps at A will be 
supplied from both directions by the feeders A and C with very 
little drop. _ If nearly all the lamps at Z were turned out, the feeder 
A could also be disconnected by opening the switch /; but if every 
lamp were put in use, or if the load on the mains happened to be 
uniform, then all three switches, /, /, and G, should be closed. 
The distribution of potential on uniformly loaded mains sup- 
plied by feeders at symmetrical points is illustrated in Fig. 34. 
Each of the mains & K and S 7 is supposed to consist of 1,800 
feet of No. 2 (A. W. G.) copper wire, and supplies ten equidistant 
groups of lamps, each taking ten amperes. ‘These mains are fed 
with current from the generator D by feeders A and 4, which lead 
to points 400 feet from each end. The portion Z/G of the mains 


f 


A 1600 t., No.0000., .08 chm. 24g5/ * oo 





[Roa neeecnacene cat eeecnee cnet (BOUL of No. pi, nfo ee serrata 


Fig. 34. Uniformly Loaded Mains and Uniformly Distributed Feeders. 


is identical with the arrangement shown in Fig. 16, and so is the 
portion 77K ; hence the distribution of potential will be the same 
as in that case, and is represented in Fig. 35, the highest pressure 
being 111 and the lowest 109 volts. With a perfectly symmetri- 
cal arrangement of the lamps, there will be no flow of current in 
either direction between G and H’; hence those sections of the 
mains could be removed without affecting the electrical conditions. 
But in case there were more lamps at one end than at the other, 
then there would be a transfer of current through G/, which 
would tend to equalize the pressure. The feeder 4 is assumed to 
consist of 1,600 feet of No. 0000 wire having a resistance of about 
.08 ohm, and carrying 50 amperes; since it supplies 5 groups of 
lamps, each taking 10 amperes. The drop upon it is 50 x .08 = 4 
volts, and the same amount for the return feeder a; consequently 
the potential at the generator D must be 111 + 4 + 4 = 119 volts. 


PARALLELS YSLEMS OF ELECTRICAL DISTRIBUTION. 68 


If the other feeder B consists of 600 feet of No. 1 wire, its resis- 
tance will be about .075 ohms, which is approximately the same, 
and would cause a similar drop. In this instance the resistances 
of two feeders are designed to be about equal by making their 





N 
119 Volts 


Fig. 35. Potential Diagram Corresponding to Fig. 34. 


cross-sections proportional to their lengths. If the feeder B were 
made of the same size wire as A, the drop upon the former would 
only be 38% = % as much, or 13 volts, in which case it should be 
supplied with 111 + 14 + 14= 114 volts instead of 119, and one 
of the following methods of feeder regulation would be required. 
The same statement applies if the currents in the feeders differ 
considerably when their resistances are approximately equal. 

Feeder Regulation by Resistance. —In such cases a feeder 
rheostat, or “feeder equalizer,” consisting simply of a variable re- 
sistance, may be placed in series with each feeder, as represented 
in Fig. 86, the current capacity of the rheostat being sufficient for 
the maximum current conveyed by the feeder. In operating such 
a system a certain amount of resistance R is introduced into the 
circuit of feeder A that is lightly loaded, in order that the pressure 
which it supplies to the mains shall not be too high compared with 
that of the more heavily loaded feeder 4, which has less resistance 
inserted. Thus by adjusting the arms of the rheostats & and S, 
the voltage at the ends of the feeders A and 4 may be made equal 
for all loads, or the potential at the outer end of B may be raised 
a little above that of A, in order to make up for the greater drop 
in the mains at # than at F- 

The voltage at the farther ends of the feeders may be deter- 
mined by running extra conductors, WW, called “ pressure wires,”’ 
from the generating-plant to the point at which the feeder is con- 


6-4 ELECTRIC. LIGHTING. * 


nected to the mains. The actual potential is read directly on the 
voltmeter V, since the current in the wires W Wis so little that 
there is no appreciable drop upon them even when they are quite 
small. Another method consists in subtracting the drop 7 FR on 
the feeders from the voltage V at the generators; that is, the po- 
tential at the ends of the feeders P = V — / R, in which / is the 
current and & the resistance of a given pair of feeders. For this 
purpose an amperemeter may be put in series with each pair of 
feeders, and it can be calibrated to give the drop upon them by 
simply multiplying its scale numbers by the total resistance of the 
two feeders. <A still more perfect device is the so-called compen- 
sated voltmeter. This has the ordinary coil which measures the 
voltage of the generators, and an additional coil that carries a cer- 





Fig. 36. Feeder Regulation by Resistance. 


tain fraction of the feeder current, the effect of the latter being to 
slighty oppose the former, so that it reduces the deflection of the 
pointer, and indicates the pressure at the outer end of the feeder. 
The objection to the resistance method of regulation is the loss of 
energy that it entails, the amount of which is represented by the 
percentage that the voltage supplied to a given feeder is lowered. 
The present practice tends toward the use of the two following 
methods of feeder regulation in preference to the two already de- 
scribed, particularly in the larger systems. | 
Auxiliary ’Bus Bars are often employed in stations or plants of — 
considerable size, in order to avoid the loss of energy which inevi- 
tably occurs when “dead”’ resistance is used for regulation. This 
method is represented in its simplest form in Fig. 387, C and D 
being two dynamos, one of which, D, is connected to the main 
"bus bar /, and generates the ordinary potential required to supply 
the shorter feeders, or those that are lightly loaded, such as B. 


PARALLALOSVSTEMS OF ELECTRICAL DISTRIBUTION. 60 


The other dynamo, C, runs at a higher voltage, and is connected 
to the auxiliary bus bar / for supplying the longer or more heavily 
loaded feeders represented by A. The scope for regulation is still 
further increased by varying the pressure at either or both of the 
‘bus bars. This may be accomplished by hand or automatically, 
rheostats in the shunt field circuits of the dynamos, compound 
winding, or other means for controlling the 4.4/7. of dynamos, 
being employed for the purpose. In this connection it should be 





Fig. 37. Feeder Regulation with Auxiliary ’Bus Bar. 


noted that the introduction of resistance in a shunt or separately 
excited field circuit involves far less loss of energy than when it 
is put in the main circuit, since the current in the former is only 
about one to three per cent of the latter. It is evident that any 
number of ‘bus bars may be used, being supplied with current by 
dynamos running at different voltages ; and two or more dynamos 
may be operated in parallel on any ‘bus bar, in accordance with 
the demands for current. It is also obvious that several feeders 
may be connected to one’bus bar. Each feeder is provided with 
switches that connect it to any particular ’bus bar according to the 
load upon it. 

A Transfer ’Bus Bar is used to enable a feeder to be gradually 
shifted from one ’bus bar to another, without the sudden variation 
in potential which would occur if it were thrown over directly by 
means of the switches mentioned above. This arrangement 1s in- 
dicated in Fig. 38, being similar to that shown in Fig. 37, but hav- 
ing a transfer bus bar P in addition to the main and auxiliary bars 
Pand. Han ines latver is connected: to. they resistance  coilsjofia 
rheostat, the movable arm JV’ of which is connected to the transfer 
bar P. The operation of shifting the feeder B from the main ’bus 
bar / to the auxiliary 4, when its load becomes large, is as follows : 
The feeder #& is connected to the transfer bar at /, the rheo- 


66 ELECTERICVLIGHIING. 


stat V being previously open circuited. The arm V is then moved 
clockwise until it comes in contact with the extremity of the 
resistance. This connects the feeder & with the auxiliary bar & 
through the whole of the resistance, and allows a certain current 
to flow from £ into 4, the former having a higher potential than 
f, to which # still remains connected. The resistance is then 
gradually cut out by the further movement of the arm V until 
the current supplied from the auxiliary & to the feeder B is equal 
to the load carried by the latter, when the connection between B 
and the main ’bus bar / is opened. The remainder of the resis- 
tance is then cut out, which directly connects the feeder # with 
the auxiliary bar “, the transfer having been made without any 
disturbance of the system. In performing this operation the 






TEEITE 





Fig. 88. Feeder Regulation with Transfer ’Bus Bar. 


amounts of current may be ascertained by having an amperemeter 
inserted between the rheostat and £ in addition to the ampere- 
meter that should always be placed in circuit with each feeder. 
The difference of potential between the feeders, ‘bus bars, etc., 
should also be indicated by voltmeters. The necessary instru- 
ments are assumed to be present in every case, but are omitted 
from the diagrams to avoid confusion, as they perform no active 
part in the operation of the system, their only function being to 
give information. 

Where two or more feeders run to the same mains, one of them 
may be transferred from one ’bus bar to another by simply open- 
ing the switch connecting it with one bar and closing an instant 
later the switch that connects it to the other. Both switches 
must never be closed at the same time, as it would short-circuit 
the potential difference between the two ’bus bars. The drop on 
a feeder being usually only a few volts, its circuit may be opened 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 6% 


with practically no greater flash than is produced by any other cir- 
cuit having a voltage equal to this drop, provided the remaining 
feeders and the mains are sufficient to carry the current without 
materially increasing the fall of potential upon them. 

Feeder Regulation by Means of ‘* Boosters ’’ is represented in 
Fig. 39, in which D is the main dynamo generating the greater part 
of the electrical energy, and & and SS are two small auxiliary dyna- 
mos called “ boosters,’ connected in series with the dynamo D and 
the two feeders A and BZ respectively. Assuming that the main 
dynamo ZY generates a constant voltage, the variation in pressure 
required to regulate the feeders in accordance with the changing 
loads upon them is obtained by controlling the potential of the 
boosters R and S. This is usually accomplished by exciting the 
field magnets of the boosters from the dynamo JV, a rheostat being 





Fig. 89. Feeder Regulation by means of ‘ Boosters.’ 


inserted in each field circuit. Another plan is to provide the 
boosters with series-wound field magnets, in which case the voltage 
generated by each increases with the current flowing throygh it. 
With field magnets designed to work below magnetic saturation, 
this gives an automatic regulation that is almost perfect ; since the 
extra pressure produced by the booster may be made to exactly 
overcome the drop on the corresponding feeder for all loads, or it 
may be designed to also make up for some or all of the drop on 
the mains and leads. The principle of this last-described method 
is quite similar to that of compound-wound dynamos ; but it acts 
upon the feeders individually, instead of upon the system as a 
whole.. It corresponds to a case where each feeder is supplied 
by its own compound generator, which is a possible but hardly 
practicable arrangement with a large number of feeders, twenty 
or thirty being an ordinary number. In any system the main 
generator and the boosters may all be driven by one or more 
steam-engines or other prime movers, or the boosters may be 


68 ELECTRIC LIGHTING. 


operated by electric motors supplied with current from the main 
dynamos. 

Similar machines are sometimes used to reduce or “crush”’ the 
voltage instead of raising it, in which case the main dynamo may 
be run at the average pressure required by the feeders, the poten- 
tial in those that are heavily loaded being increased, and being 
depressed in the lightly loaded ones. A “crusher” which lowers 
the voltage by generating a counter 4.J7./. acts as a motor, and 
tends to develop power; consequently, if it is coupled with a 
booster, it will drive the latter as a dynamo, provided that the 
energy absorbed by the former is slightly greater than that pro- 
duced by the latter, in order to make up for mechanical and elec- 
trical losses in both machines. By thus arranging the machines 
in pairs, they run each other, and no external driving-power is 
needed. 

Instead of having a separate booster for each feeder, as in- 
dicated in Fig. 39, two or more feeders requiring approximately 
equal voltages may be supplied from the same booster. In this 
way a large number of feeders may be regulated with only a few 
boosters, which are run at different potentials, the feeders being 
divided among them according to the extra pressure required. 
This is practically equivalent to a system having several auxiliary 
*bus bars supplied with different voltages. In Fig. 37, for exam- 
ple, the dynamo C might be omitted, and the higher voltage 
required for the auxiliary bus ‘bar & could be obtained by connect- 
ing a booster between & and /2« This 1s often preferable; "since 
it would only be necessary to run one main dynamo, the booster 
being driven by a motor fed with current from the dynamo. 

The arrangement represented in Fig. 40 combines several of 
the methods of feeder regulation already described. The genera- 
tors C and D operating in parallel are connected to the "bus bars 
/ and H, to which they supply the ordinary voltage required by 
the feeders. The conductor £, called the “zgh auxzliary ’bus bar, 
is maintained at a higher potential than / by means of the booster 
A. The conductor G receives its current from the main ‘bus & 
through the resistance 4, consequently its pressure is less than 
that of /; and it is designated as the low auxiliary ’bus bar. 
The teedérs:/, A, and J are connected io 4,-7.0) G accor 4.0 
the voltage that they require, the longest and most heavily loaded 


PARALLEL SYSTEMS OF ELECTRICAL DISTRIBUTION. 69 


being fed by the high auxiliary £, which is often 10 or 20 per 
cent and sometimes 40 or 50 per cent higher in pressure than the 
main ‘bus /, The amount of this extra voltage is regulated by 
means of a rheostat in the field circuit of the booster A, usually 
excited from the ’bus bars # and H. If the dynamo C be con- 
nected to & and not to /, the higher pressure may be generated 
by it, and the booster.A can be dispensed with, as already shown 
in Fig. 37; but it is often more convenient to operate all the main 





Fig. 40. Feeder Regulation by a Combination of Methods. 


generators in parallel on the same pair of ’bus bars, and obtain the 
higher and lower potentials, if required, by means of boosters and 
resistances. The latter, on account of their simplicity, are applic- 
able when the differences in pressure are small, the voltage of the 
low auxiliary ’bus G in Fig. 40 being between 5 and 10 per cent 
less than that of /, for example. But with greater reductions the 
loss of energy becomes too large an item, and it is more econom- 
ical either to run another generator or a “crusher” (with counter 
fon Py LO supply. GC. 


a 


70 ELECTRIC LIGHTING, 


° 


GigGe we Fisker e 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 


THE three-wire system, which was independently invented by 
Edison and Hopkinson, has for its object the saving of copper in 
distributing conductors. From the first introduction of electric 
lighting until about 1897, it was not considered practicable to use 
incandescent lamps designed for a pressure higher than 120 volts. 
This limited the potential at which parallel systems were operated, 
and demanded conductors of large size and weight, particularly 
when the current is transmitted any considerable distance, as 
already shown in the examples given. When it is attempted to 
supply incandescent lamps in series, difficulties immediately arise, 
due to the dangers of high potential, the interference between the 
lamps, and the imperfection of regulation, all of which were noted 





Figs. 41 and 42. Evolution of the Three-Wire System. 


in Chapter II. The principle of the three-wire arrangement may 
be understood by first considering two entirely distinct two-wire 
circuits, as represented in Fig. 41. If the lamps Z and WV happen 
to be placed in the manner shown, it is evident that they may be 
connected,in series of two each, as illustrated in Fig. 42, in which 
case the intermediate wires / and K become superfluous and are 
omitted. But when one of the lamps is turned off or burned out, 
its companion will also go out ; hence a third wire, indicated in Fig. 
43 by a line marked 0, is extended from the junction between the 
two dynamos C and J in order to avoid the difficulty. This allows 
any number of the lamps to be disconnected without putting out 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. T1 


those which remain. The extra conductor is called the neutral 
wire, and is usually marked 0 or +, the latter symbol represent- 
ing the fact that it is positive with respect to one conductor and 
negative with respect to the other. The neutral wire carries no 
current if the system is exactly “balanced” (Fig. 43); but when 
the amounts of current on the two sides of the system are not the 
same, it supplies the difference, whatever it may be, as represented 





Figs. 43 and 44. Three-Wire System. 


by arrows and numbers in Figs. 44 and 45, each lamp being 
assumed to take one ampere. 

It should be observed that the flow of current may be opposite 
in direction in different parts of the neutral wire (Fig. 44). An- 
other peculiar condition in three-wire circuits is the fact that the 
potential at certain lamps may actually be higher than that of the 
dynamo on the same side of the system. This is demonstrated in 
the potential diagram (Fig. 46), corresponding to the arrangement 







+44 volts drop 
117|volt 
volts 3 volts drop 110 ue 
S) re) 3 
119] volts 


1 volt drop 





Figs. 45 and 46. Three-Wire System. 


of .amps shown in Fig. 45. Assuming the resistance of each of 
the three wires to be 1 ohm, the drop on the + conductor between 
Rand M will be 4 volts with a current of 4 amperes. The drop 
between /V and S on the neutral wire will be 3 volts, since 3 am- 
peres flow back through it. With a potential of 117 volts at each 
dynamo, this gives 110 volts for the lamps between J/ and JW. 
The drop on the — wire between P and 7 is 1 volt, hence the 
potential of the point P is 1 volt above that of 7; but as WV is 3 
volts higher in potential than 5S, it follows that the pressure be- 


pe ELECTRIC LIGHTING. 


tween JV and P is 2 volts greater than that delivered at S and 7 
by the dynamo D. Therefore the lamps at JZ J receive 7 volts less 
pressure, and the lamp at VV P is supplied with 2 volts more pres- 
sure than the potential difference at the respective generators. 
While this condition is possible, it is not likely to occur in practice, 
particularly in large systems, where the circuits are carefully bal- 
anced. In such cases, the difference in the total load on the two 
sides of the system is often as small as 2 or 3 per cent. 

Advantages and Disadvantages of the Three-Wire System. — 
The sole merit of this arrangement is the fact that it saves copper, 
the amount of this saving being determined as follows : — 

The circuit represented in Fig. 42 has two wires, while those 
in Fig. 41 employ four ; hence the former requires one-half as much 
copper as the latter, assuming the size of the wires to be the same. 
Furthermore, the percentage of drop in Fig. 42 will only be one- 
half as great as that in Fig. 41, the explanation of this fact being 
given in Figs. 47 and 48, which show the distribution of potential 
in the two cases. In the two-wire circuits (Figs. 41 and 47) there 
will be a drop of 4 volts on each wire, assuming 4 amperes of 
current and one ohm of resistance for each ; and the lamps will re- 
ceive 106 volts with a pressure of 114 volts at the dynamos, the 
drop being ;%z, or 7 per cent. 

The lamps on the three-wire circuits (Figs. 42 and 48) receive 
110 volts with the same initial potential, i.e., 114 volts, the drop 
being only +4 or 3.5 per cent, which is one-half as much as in the 
previous case. It follows, therefore, if the wires in Fig. 42 have 
one-half the cross-section of those in Fig. 41, that the percentage of 
drop will be the same for both. Consequently Fig. 42 requires one- 
half as many conductors of one-half the size, or only one-quarter 
as much copper, as Fig. 41 for the same drop. If now the neutral 
conductor in the three-wire system (Fig. 43) be made the same 
size as each of the outside wires, the weight of the copper will be 
} + } = $ as much as in the two-wire circuits (Fig. 41) supplying 
the same number of lights at the same distance with equal drop. 
Since the neutral wire usually carries only a small current, it is 
often made (especially in feeders) one-half as large as either of the 
outside conductors, in which case the weight of copper becomes 
yj’; that demanded by the two-wire system. 

The great saving in copper, amounting ordinarily to % or 62.5 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 13 


per cent, is considered of such paramount importance that the 
three-wire system is usually adopted in electric lighting for low- 
tension distribution wherever the distances are considerable. In 
the case of low-tension central stations this custom is very general, 
and even for large isolated plants the three-wire system is often 
selected. It is also employed in many instances for the secondary 
wiring in alternating-current distribution with transformers. The 
object in all cases is to save copper, which constitutes such a large 
item in the cost of nearly all electrical installations. 

To offset this advantage, however, the three-wire system has 
the following disadvantages : — 

1. It is usually necessary to operate at least two dynamos or 
other sources of current. ) 

2. It is necessary to lay and to take care of three wires instead 
of two. 

3. The switches, cut-outs, measuring instruments, etc., are also 
more complicated. 

4. The saving of copper stated, assumes that the neutral wire 
carries no current. 

But if all the lamps happen to be in use on one side of the sys- 
tem only, the copper should be the same as for a two-wire circuit. 


4 volts drop 4 volts drop 


+ 


414] volts 106} volts 114] volts 110{volts 
4 volts drop 


4 volts d “ 
Olts drop 2 ‘ 
volts 106|volts 114] volts 110\volts 
4 volts drop 4 volts drop 


Figs. 47 and 48. Three-Wire System. 












114 


Even though the system be kept balanced as carefully as possible, 
so that the current in the neutral conductor is only 10 per cent of 
the total, the saving of copper would be reduced from 62.5 to about 
50 per cent for the same actual percentage of drop. 

5. The variation in potential may be aggravated by the increase 
that sometimes takes place (Fig. 46), which is impossible on a 
two-wire circuit. 

When all these objections are considered, it is somewhat doubt- 
ful if the reduction in the weight of copper makes up for them in 
some cases where the three-wire system is adopted. There is a 
strong tendency on the part of the purchaser, consulting engineer, 


(4 ELECTRIC. LIGHTING. 


and contractor to give too great weight to the matter of first cost, 
and too little heed to questions of convenience, labor involved, lia- 
bility of accidents, and many other factors that make up running 
expense. The three-wire system is unquestionably more compli- 
cated and difficult to install or operate, and it should not be selected 
unless the saving that it secures is surely sufficient to pay for these 
disadvantages. For low-tension distribution to distances of a mile 
it has been considered necessary to employ it ; but for isolated plants, 
where the length of wires is only a few hundred feet, its superiority 
is by no means certain, in spite of the very powerful argument 
which may be based upon the saving of copper. 

The improvements in and applications of 220-volt incandescent 
lamps render the three-wire system considerably less important 
than formerly, since it enables a two-wire circuit to be operated at 
220 volts, the copper required being only two-thirds as much as 
for the ordinary three-wire system. To be sure the latter can now 
be run at 440 volts, giving it the same relative advantage as before ; 
in fact, such plants are now being installed in this country and 
abroad. Many five-wire systems are being changed to three-wire, 
with 220-volt lamps. 


MODIFICATIONS OF THE THREE-WIRE SYSTEM. 


Three-wire System with Double Dynamo. — Various arrange- 
ments have been used or proposed as substitutes for the ordinary 
plan of using two generators. One of these, outlined in Fig. 49, 
employs a double dynamo J, 
having two armature windings 
upon the same core, connected 
to two separate commutators 
CC. This double generator is 
used in the same manner as 
the two generators in Fig. 48, 

Fig. 49. eee System with Double and may save floor-space as well 
ynamo. 
as the trouble of running two 
machines, but no great advantage is secured. 

Bridge Arrangement of Three-wire System. — Probably the first 
method of operating a three-wire circuit by means of a single gen- 
erator was the bridge connection devised by Edison.* The plan 





* U.S. Patent No. 343,017, June 1, 1886. 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. (5 


is indicated in Fig. 50, and consists simply in connecting a resis- 
tance RA across the outside conductors + and —, the neutral. 
wire 0 being brought to a point 


‘on the resistance through the nf 
movable switch-arm S. The es | 0 
objections to this method are, S 
first, the continuous loss of en- be 
ergy that occurs through the Fig. 50. Bridge Arrangement of Three-Wire 


: System. 
resistance A.A, and second, the 


fact that the arm S must be adjusted for any change in load, in 
order to equalize the pressures on the two sides of the circuit. 
Three-wire System with Storage Battery. — This modification, 
illustrated in Fig. 51, requires only a single dynamo, VP, generating 
the total pressure for both sides of the system, which is usually 
about 230 volts. <A storage battery, 44, is connected between the 
two outside wires + and —, the neutral wire 0 being led to the 
middle point of the battery. In cases where it is advantageous to 
employ a battery to equalize the load on the engines, or for other 
reasons, this plan is a convenient one, since it only necessitates 
the running of one dynamo. The potential of the neutral wire 0 
may be varied to make up for differences in load on the two sides 
of the system by shifting the point at which it is connected to the 
battery. If the difference of potential between the two outside 
conductors is greater than the F.J/F. of the battery, the latter 
will be charged, and wice versd, the same as in a two-wire system. 
With a three-wire circuit it is also possible for one part, A, of the 





Figs. 51 and 52. Three-Wire Systems. 


battery to be discharging while the other part, 2, is charging. 
This may occur if there are a great many lamps on the + side, 
and very few on the — side. The function of the battery is to 
act as an equalizer, taking or giving current, as required, and keep- 
ing the potential of the neutral wire approximately half way be- 
tween the potentials of the + and — conductors. The fall in 
voltage during discharge and the rise during charge, amounting to 


TO ELECT RIG TL ie 


three-tenths of a volt or more, being nearly 15 per cent, and the 
difference between the charging and discharging pressures, make 
it necessary to employ extra cells and switching-devices, or means 
of regulation, such as are described in Volume I, page 397. A 
differential booster may also be used to automatically generate the 
extra voltage required to charge the battery. | 

The storage battery represented in Fig. 51 can be placed at a 
distance from the generator, and connected to it by two feeders, 
three wires being required only for the local distribution. This 
arrangement also enables the current on the feeders to be made 
more uniform, the battery being charged during periods of light 
load, and discharged when the demands for current are great. 
This permits feeders of smaller size to be used, and also reduces. 
the variations in load on the generating plant, so that the latter 
operates more efficiently, and can be designed for less capacity 
than the maximum load. But extra expenses for attendance, rent, 
etc., are involved at the sub-stations. 

Three-wire System with Three-brush Dynamo. — Fig. 52 indi- 
cates another three-wire arrangement that can be operated with 
only one generator, D, the neutral wire being connected to a third 
brush, /, placed half way between the main brushes £& and G, to 
which the outside wires + and 
— are respectively attached. 
With most types of dynamo 
the brush / would spark ex- 
cessively because it short-cir- 
cuits the armature coils when 
they are generating the maxi- 
mum E.M.F. There are sev- 
eral ways to avoid this difficulty, 





Fig, 58. Three-Wire System with One Dynamo. | one of which consists in employ- 

ing a four-pole dynamo, shown 
in Fig. 538, having two adjacent north poles, Vand J, the other two 
being south poles, S and S. The machine thus becomes in effect 
a bipolar dynamo with each pole divided, the armature coils short- 
circuited by the brush / being in the space between the two halves. 
S and S of the south pole, where they generate little or no L.AZF. 
A dynamo to be used in this way requires a field-magnet ring of 
sufficient cross-section between the WV and S poles (i.e., at the top 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. (as 


and bottom in Fig. 53) to carry the total magnetic flux of one field 
core. In an ordinary multipolar machine with alternate V and S 
poles, this ring need have only one-half as much sectional area. 
Since practically no flux passes through the two sides of the field 
ring they might be greatly reduced in size, but this is limited by 
considerations of strength and appearance. The radial depth of 
the armature core must also be sufficient for the total flux of ‘one 
field core. The extra quantity and less favorable disposition of 
material in the generator is not a very serious matter, however ; 
and this plan of operating a three-wire system would often be a 
very practical and convenient one for small plants. 

There is, however, with this arrangement, the difficulty that 
armature reaction tends to increase the flux in the lower S pole, 
and reduce it in the other, hence with heavy loads the voltage on 
the + side of the system would be less that on the — side. This 
can be counteracted by compound winding on the upper S pole, 
and differential winding on the lower S pole. Another brush could 
be placed between the two WV poles, and connected in parallel with 
fF; but since the neutral wire only carries a comparatively small 
current, one brush would ordinarily be sufficient, the main portion 
of the current being supplied through the brushes & and G. 

Dobrowolsky Three-wire System. — Another method of operat- 
ing a three-wire system by means of a single dynamo invented by 





Fig. 54. Dobrowolsky System with Self-Induction Coil. 


von Dolivo-Dobrowolsky * is represented diagrammatically in Fig. 
04, It consists of an ordinary direct current generator, the arma- 
ture A and pole pieces V and S of which are shown. A  self-induc- 
tion coil, D, is connected to two diametrically opposite points of the 
winding of the armature A. The coil D may be carried by and 


* U.S. Patent, No. 513,006, Jan. 14, 1894. 


78 ELECTRICOL/IGHENG, 


revolve with the armature ; but in the construction represented it is 
stationary, being connected to the armature winding through the 
brushes CC, rings and wires //, The middle point of the self- 
induction coil Y is connected to the neutral conductor 0 of the 
three-wire system, the outside conductors + and — being supplied 
from the brushes 24 inthe Usual#manner, )) The feat tie 
terminals of the coil J is alternating ; hence the latter, on account 
of its self-induction, does not act as a short-circuit to the armature. 
Furthermore, the inductances of the two halves of the coil D being 
equal, the potential of the neutral wire 0 is kept midway between 
the potentials of the outside wires + and —. When the two 
sides of the system are unbalanced in load, the difference in cur- 
rent carried in one direction or the other by the neutral wire 
passes freely through the coil J, since the current is steady, or 
varies slowly, and is therefore unimpeded by the self-induction. It 
is evident that the ohmic resistance of D should be as low and its © 
self-induction as high as possible, in order that the loss of energy 
and the difference in voltage on the two sides of the system shall 
be as small as possible under all conditions. 

Three-wire System with Auxiliary Generator. — In the three- 
wire system represented in Fig. 55 the neutral wire 0 is connected 





Figs. 55 and 56. Three-Wire Systems. 


to an auxiliary machine 4 which supplies a potential one-half as 
great as that of the main dynamo D. The machine 7 acts as a 
generator when the — side requires more current than the + side, 
but it runs as a motor when the current on the + side is greater. 
Hence it should be belted to or directly coupled with the dynamo 
D, in order to save its power when acting as a motor. The machine 
ff, being intended to carry only the difference between the cur- 
rents on the two sides of the system, may have only 5 or 10 per 
cent of the capacity of the dynamo D. This is sufficient as long 
as the sides are fairly well balanced, but is entirely inadequate if 
the difference becomes great, which may easily occur by accident. 
The ordinary three-wire arrangement, or that shown in Fig. 52, 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 19 


has the advantage of being able to operate, if necessary, with a full 
load on one side and none on the other, which might occur if there 
was an open circuit on one of the outside wires, due to the blowing 
of a fuse or to some other cause. 

The same statements apply to the storage battery in Fig. 51, 
which may be designed to have a capacity equal to the full load or 
only a fraction of it. 

Three-wire System with ‘‘Compensators’’ is represented in 
Fig. 56, in which the two auxiliary machines J7/ and J are mechani- 
cally coupled together, and each eenerates one-half as much pressure 
as the main dynamo JY, These machines are called compensators or 
equalizers, and serve to equalize the pressure and load, the one on 
the more lightly loaded side running as a motor, and driving the 
other as dynamo. Hence they are capable of operating with a dif- 
Terence imspower onithe two, sides of the circuit equal to. their 
combined capacity. When the system is perfectly balanced, both 
machines run as motors without load, and consume very little 
energy. 

This combination involves three machines in place of the two 
dynamos required in the ordinary three-wire system ; nevertheless, 
it is very commonly and successfully used, being in many cases 
decidedly preferable. The two machines 7 and J are entirely 
self-acting, driving each other mechanically and maintaining equal 
voltages, with very little attention or likelihood of trouble. They 
are in most cases more easily operated than a second dynamo, and 
the friction as well as other losses are usually less. — _ 

If both armature windings are upon the same core, armature 
reaction is neutralized, and the tendency to sparkling greatly re- 
duced. A still more important advantage is the fact that the 
double machine J7N can be placed at any desired distance from 
the generating plant and connected to it by two feeders, three wires 
being required only for the local distribution, as already stated in 
reference to Fig. 51. It is also possible to run a “booster” or 
small auxiliary dynamo by means of the compensating machines. 
M and J, in order to raise the pressure of the circuit a certain 
amount, and make up for drop on the conductors. An arrangement 
of this kind, illustrated in Fig. 57, requires only one “booster,” 2, 
for both sides of the system. The compensating machines J/ and 
NV are connected to the outside conductors at the points R and S 


80 ELECTRIC LIGHTING. 


beyond the booster 4, and therefore have the increased difference 
of potential, which they subdivide in two equal parts for the two 
sides of the system. The three machines 4, J, and JW are me- 
chanically connected together by direct coupling or belting. | 

The field magnets in Figs. 55, 56, and 57 may all! be excited 
by simple shunt winding connected to the brushes of each machine 
respectively. It is preferable, however, to feed all the field coils 
from the main current supplied by the generator JD, since that 
makes each machine less likely to aggravate variations that occur 
in its own portion of the circuit. The shunt coils of the compen- 
sators WN in Figs. 56 and 57 may be connected in parallel or in 
‘series to the outside wires + and —. The field coils of the booster 





Fig. 57, Three-Wire System with Compensator and Booster. 


B in Fig. 57 may also be fed from the main conductors + and —, 
in which case its voltage would be regulated by hand, using a varia- 
ble resistance in the field circuit. If, however, it were provided 
with a series winding through which the main current of the + 
conductor passed, the extra pressure produced by it would auto- 
matically increase with the current as described in reference to 
feeder regulation in Fig. 39. 

If the strength of the fields in the machines J/7 and WV (Figs 
56 and 57) are capable of being independently regulated, the vol- 
tages on either side of the system may be varied to make up for 
differences in load, the pressure being made somewhat higher on 
the more heavily loaded side to counterbalance the greater drop 
on the conductors. This regulation can be made automatic by the 
arrangement represented in Fig. 58. The main generator D is 
assumed to be sufficiently over-compound wound to make up for 
the total drop on the conductors. Additional control of the vol- 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 81 


tage may be obtained by adjusting the variable resistance R in 
the shunt field circuit. The compensating machines J7 and J, 
mechanically coupled as before, are also compound wound. The 
effect of the series field-coils P is to cause the machine on the heav- 
ily loaded side to produce a higher voltage, and the one on the 
more lightly loaded side a lower voltage, whereby the difference 
in drop is equalized. Assuming three lamps, each taking one am- 
pere on the + side and one lamp on the — side, the dynamo D 
will supply two amperes, as indicated by arrows and figures, the 
machine /7 will generate one ampere additional, being driven by 
the machine JV acting as motor, and using one ampere. The cur- 
rent in the series field-coils P increases the £.J/.F. of M, and 





Fig. 58. Three-Wire System with Compound-Wound Boosters. 


decreases the counter E.J7/. of J, since it flows in a reverse 
direction in the latter; hence the difference in drop on the wires 
between the compensator J7NV and the lamps may be equalized 
» provided the compound winding is properly proportioned. 

~~. Conversion from Three- to Two-wire System. — A three-wire 
system of conductors can readily be connected so that it may be 
used as an ordinary two-wire circuit. For this purpose the two out- 
side wires are connected to one terminal, and the middle wire to 
the other terminal of the generator, as represented in Fig. 59. The 
lamps are fed between the middle conductor and either of the 
others, but the direction of current is reversed in all of those that 
are on one side of the system. This makes no difference in the 
operation of incandescent lamps, but would require the connec- 
tion of arc lamps to be reversed, the same being true of storage 


82 ELECTRIC LIGHTING. 


batteries, electroplating cells, or other electro-chemical apparatus 
that may be on that side of the system. Some forms of meters, 
and other measuring instruments, would also be reversed in action. 
Motors running on either side of the circuit would not be affected, 
since the direction of rotation is not changed by reversing the cur- 
rent in both armature and field coils. But a motor or other device 
connected across the outside wires, which is the usual arrangement 
for the former, would receive no current, because these wires are 
of practically the same potential when used in this way. 

The drop on the conductors is greatly increased by conversion 
to the two-wire arrangement. In a perfectly balanced three-wire 
system there is practically no current or drop on the middle wire ; 
but when used as a two-wire circuit, the current and drop on this 
conductor is twice that in 
either of the others, conse- 
quently the total drop is 
three times as great as be- 
+)" fore® Uhissassumes*thaterne 

middle wire is the same in 
size as either of the others. 
If it is only one-half as large, then the drop in it would be four 
times as great as in one of the outer conductors, and the total 
drop five times as much as in a balanced three-wire system. 
There is also danger of blowing the fuses on the middle wire, or 
overheating it, unless it is specially designed to be used in this way. 

There are two cases in which the conversion from the three- 
to the two-wire system is commonly practiced. First, a small 
station, or isolated plant, which is operated on the three-wire plan 
when heavily loaded, and on the two-wire plan for light loads, one 
dynamo being sufficient in the latter case, and the drop on the con- 
ductor then being quite small. Second, an isolated plant, which is 
supplied by its own generator most of the time, but is connected 
to the three-wire “street circuit’ (.e., central station conductors ) 
during certain portions of the day or night, or in case its machin- 
ery is disabled. On account of the latter contingency the name 
“breakdown switch” is applied to the device which connects the 
wiring inside the building with the outside conductors. This 
switch may be so made that it simultaneously opens the connec- 
tions with the local generator. 





Fig. 59. Conversion from Three-Wire to 
Two-Wire System. 


—,_ 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 88 


OPERATION OF THREE-WIRE SYSTEMS. 


The general arrangement of three-wire feeders and mains may 
be made substantially the same as already described for the two- 
wire system, the same methods and care being used in regulating / 
the voltage. The feeders may consist of three conductors of the | 
same size; but usually the neutral feeder is made } or } as large | 
as either of the others, and if storage batteries or equalizing ma- 
chines are placed at the outer ends of the feeders, the neutral con- 
ductor may be omitted, as previously explained (Figs. 51 and 56). 
For the mains and leads the three wires are generally made the 
same in size. The important point in connection with the three- 
wire system is the necessity for carefully dalancing it ; that is, 
keeping the currents on the two sides approximately equal. To 
accomplish this the lamps and other devices requiring current are 
divided between the two sides of the system, so that the loads shall 
be as nearly as possible the same for full capacity or any fraction 
of it. For this reason all three wires should be carried to any point 
where energy is required, unless the amount is extremely small. 
This applies to every building, even though it contains only a few 
lamps, and in fact to almost every room that is to be supplied with 
current. In this way the chance of having any considerable differ- 
ence in load is reduced to a minimum. 

Nevertheless, it is possible that a great many lamps might hap- 
pen to be lighted on one side of the system and very few on the 
other side, in which case the drop in voltage would have about 
twice its normal value for the larger number of lamps, while the 
pressure might be raised for the smaller number, as already ex- 
plained (Fig. 46). The likelihood of this happening is small, 
however, particularly in large systems, provided the lamps are 
carefully divided in wiring them. In case many lamps are to be 
lighted at the same time, they should be controlled by three-pole 
switches, which connect them to the two sides equally, or they 
should be divided into groups that are thrown on the sides alter- 
nately. 

It is not sufficient in a three-wire system to have equal num- 
bers of lamps on the two sides, they must also be distributed in 
approximately the same manner. For example, with a group of 
lamps requiring 100 amperes connected between the + and 0 


84 ELECTRIGCOLIGCAHLING. 


wires at one point and an equal load between the 0 and — wires 
some distance away, there would be a current of 100 amperes 
flowing on the 0 wire between those points. This involves con- 
siderable extra drop, although the system would appear at the gen- 
erating station to be perfectly balanced. In practice this local 
unbalancing of the three-wire system is one of the chief causes 
of variations in voltage upon it, and should be made as small as 
possible by carefully distributing the load on both sides of the 
system. It is this fact which renders it desirable to carry all three 
wires to almost every place where current is required, even though 
a fair balance in the total load might be obtained by supplying 
buildings alternately from the two sides of the system. 

Grounding the Neutral Conductor. — A question that has aroused 
much discussion is the advisability of purposely grounding the 
neutral conductor of a three-wire system. The two principal ar- 
guments in favor of this plan are: First, it practically limits the 
potential between any point on the system and the earth to about 
110 volts; second, it reduces the drop on the neutral conductor, 
since the current can also flow through the earth. In regard to 
the first of these reasons, it is a fact that the potential of the posi- 
tive wire may rise to 220 volts if the negative wire becomes 
grounded, or wzce versé when the neutral wire is insulated. But 
it can hardly be said that trouble would be avoided if the neutral 
were grounded, as an accidental ground connection on either of 
the other sides would make a short-circuit and blow the fuse, 
thus putting out the lamps on that portion of the circuit. To be 
sure this locates the trouble, and calls for immediate attention, 
which may be a simple, but is also a crude way to keep the cir- 
cuits clear of faults. If an accidental ground connection exists 
on one of the conductors when the neutral wire is not grounded, 
no trouble results until another ground occurs on one of the other 
two conductors. In the meantime an opportunity is afforded to 
correct the fault before any interruption of service or difficulty of 
any kind is experienced. 

Unfortunately it is very troublesome to detect and locate a 
ground connection even on a two-wire circuit, and still more so 
with three wires. Nevertheless, there are methods which will ac- 
complish this result ; and if these were more generally used, they 
would be found to afford reasonably practical and convenient 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 89d 


means of taking care of three-wire systems. But these methods 
fail; in fact, the problem is practically impossible to solve if the 
neutral wire is grounded. This matter will be discussed further 
in the chapter on Detecting and Locating Faults. 

Regarding the second advantage of grounding the neutral con- 
ductor, it may be said that it is well enough to use the earth to re- 
énforce the conductance of the circuit, provided no serious difficulty 
results. But it is found that great damage is done by electrolytic 
action on gas, water, and other kinds of pipes, if large currents are 
allowed to flow promiscuously through the earth. In the case of 
electric railways with overhead trolleys, it is necessary to allow the 
current to pass into the track, or else adopt the double-trolley sys- 
tem, which is complicated, and not considered practicable for general 
use. But even for the trolley system the tendency is to demand 
more perfect bonding of the rails, and the use of return feeders to 
reduce the stray currents. In electric lighting there is no neces- 
sity for intentionally grounding the circuit or any portion of it, but 
it is generally recommended for the secondary circuit of a trans- 
former, as a safeguard in case the high-tension primary circuit 
accidentally connects with the secondary. 

Insurance and fire department authorities have been vigorously 
opposed to grounding the neutral of a three-wire system, or, in fact, 
any part of an electrical circuit, their experience having led them 
to believe that it is the source of danger and trouble. This prac- 
tice is not so strongly opposed at present, and is being more gen- 
erally adopted, as nearly all central station officers would prefer to 
ground the neutral conductors. 

Peculiar Conditions on a Three-wire System. — The following 
cases may occur :— 

1. The dynamo or dynamos on one side of the system may be 
accidentally reversed, so that both of the outside wires are positive 
or both negative. In that case a motor or other device fed by the 
two outside conductors will receive no current ; but lamps, etc., con- 
nected between the neutral and either of the outside wires, will have 
the usual voltage, which will be reversed on one side. 

2. If one of the outside wires is open at B, Fig. 60, due to the 
blowing of a fuse or other cause, a motor, JZ (220-volt), beyond 
the break &, will receive some current at 110 volts through any 
lamps Z that may be on the same side of the break as the motor, 


86 FLECTRICWAIGATING. 


and on the same side of the system as the break. These lamps 
will light up when the motor is connected, but the latter will have 
comparatively little power. 

3. If the neutral wire is open, a motor or other device con- 
nected to the outside wires will act as usual, but lamps on one side 





Figs. 60 and 67. Peculiar Conditions on Three-Wire System. 


of the system will burn more brightly than those on the other side, 
unless the two sides are exactly balanced. 

4. If one of the outside wires, Fig. 61, becomes grounded at 
P,a110-volt lamp, Z, or other apparatus, also grounded and con- 
nected to the other outside wire, will receive 220 volts, which is 
likely to destroy it. 


FIVE-WIRE SYSTEMS. 


The principle of the three-wire system may be extended, in order 
to effect a still greater saving of copper in electrical distribution. 
It would be possible, for example, to have a four-wire system. re- 
quiring two-ninths as much copper as an equivalent two-wire cir- 
cuit ; but, for reasons to be given later, it has rarely, if ever, been 
tried. The five-wire system is employed in many places in Europe, 
but has not been introduced to any extent in this country. It may 
be operated with four dynamos, C, D, £, and F/; as represented in 
Fig. 62; but the arrangements shown in Figs. 63 and 64 are more 
common. The second of these is similar to the three-wire system 
illustrated in Fig. 56, only one main dynamo, VD, being required ; 
and the total pressure generated by it, ordinarily about 440 volts, 
is subdivided by the four small equalizing machines or compensa- 
tors, /, K,Z,and 17. These may consist of four separate machines 
mechanically connected together, or they may be made with all of 
their armature windings upon the same core and acted upon by one 
field magnet, in order to neutralize the effects of armature reaction. 
Fig. 63 shows a combination similar to the three-wire system 
represented in Fig. 51, a battery, 4, P, Q, FR, being utilized to 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. 8&7 


subdivide the voltage of the main dynamo Y. The conductors are 
designated, as shown in Fig. 62, the two extra wires being called the 
“positive neutral”’ ® and the “negative neutral” © respectively. 

The comparative weight of copper required for the five-wire 
system may be determined by reasoning similar to that used in 
connection with the three-wire diagrams (Figs. 47 and 48). But 
it can be arrived at more simply by considering that the current 
in each of the outside wires: of a perfectly balanced five-wire sys- 
tem is one-quarter as much as in a two-wire circuit supplying the 
same number of lamps. Hence the drop is only one-quarter as 
great, assuming the conductors to be of the same size. But since 
with five wires there are four sets of lamps in series, the percentage 
of drop is } x } = yp, as much, or in other words, each conductor 
need be only one-sixteenth as large for the same percentage of 
drop. Therefore the two outside conductors of the five-wire sys- 
tem weigh one-sixteenth as much as those of an equivalent two- 





Figs. 62 and 63. Five-Wire Systems. 





wire circuit, and the five conductors weigh § x ys = 3% as much, if 
all are made of the same size. By making each of the three in- 
termediate wires one-half as large as each of the outside ones, the 
total weight is reduced to ps + 3 X 3g = gz, or less than one-eighth 
as much copper as the two-wire circuit demands. The various 
results that have been obtained may be recapitulated as follows :— 


COMPARATIVE WEIGHTS OF COPPER REQUIRED. 


Ord ina lyatwor wih, SySteM) U.ie¢ a). % sy) fig eo see ER tY flew) de 221.000 
Three-wire system, all three wires of same size §.. . > .  .375 
(chree-wire, system, neutral one-half size. 0). .. . 313 
Four-wire system, all four Wires of same'size™ 2 2%... 6222 
Five-wire system, all five wires of same size. . . . 2. . «156 
Five-wire system, three inside wires one-half size . . . . .109 


Seven-wire system, all seven wiresof same size . . . . .097 


88 ELECTRIC LIGHTING. 


It is evident that similar systems having a greater number of 
wires might be designed, but they would be extremely complicated, 
and of very doubtful advantage. In fact, the desirability of a five- 
wire system is questionable, since the use of 220-volt lamps ena- 
bles three-wire circuits to be operated at 440 volts. <A five-wire 
system calls for an even more perfect balance of load than is 
needed for three-wire circuits. This is secured by carefully divid- 
ing the lamps, etc., between the four parts of the system so that 
the loads may be as nearly equal as possible at all times. To this 
end all five wires should be carried wherever any considerable 
amount of energy is likely to be used, as represented at A in Fig. 
64. If the demand for current is small, it is only necessary to run 





Fig. 64. Five-Wire System. 


three wires, as shown at 4. But in this case an approximately 
equal load, P, should be connected to the other side of the system, 
as near 1B as possible. (For awery small loads, 2, 2, 7, candis at 
may be allowable to put them on the separate parts of the systems, 
provided they are equally distributed, and not far apart, as repre- 
sented. Motors should generally be supplied from the two out- 
side wires (440 volts) as indicated at VV; but if they are not large 
they may be connected to the + and 0 or to the 0 and — con- 
ductors (220 volts) at B or P, and very small machines, such as 
fan motors, may be connected to adjacent wires (110 volts) at & 
or k. Arc lamps may be arranged as shown at / and S, or a 
suitable number may be put in series across the outer wires at 4 
or B. 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION, 89 


The flow of the currents and values of the potential in five-wire 
systems may be determined by extending the methods: already 
explained in connection with three-wire circuits. Although appar- 
ently a complicated matter, a problem of this kind can be solved 
without much difficulty in most cases. In practice the current to 
be supplied is usually known, or its probable value may be assumed. 
A diagram similar to Fig. 65 should then be made, showing the 
arrangement of circuits and distribution of current. It is much 
simpler, and in most cases sufficiently accurate, to consider the 
lamps or other apparatus requiring energy to be located in groups, 
approximating as closely as possible their actual positions. 

This enables the conductors to be divided into sections, in each 
of which the current is uniform, as represented in Fig. 65. The 





+000-FT-NO-10——1-OHM-RESIS- 


<———10 AMP. <— — 5 AMP. 


Fig. 65. Distribution of Current in Five-Wire System. 


determination of the amount and direction of the currents in the 
various sections is easily made. If 10 amperes are required at # 
and also at / it follows that that amount of current will flow out 
on the + wire, and half-way back on the © wire, there being no 
current in the rest of this conductor. Since 5 amperes are required 
at G, one-half of the 10 amperes will flow out to that point, and 
the other 5 amperes will return to the dynamo through the O 
conductor, the function of the three neutral or.intermediate wires 
being to carry the difference between the currents used in the ad- 
jacent portions of the system, whatever its amount and direction 
may be. 

The 5 amperes required at HY are supplied by the © conduc- 
tor, and the 5 amperes used at / by the same current that flows 
through G, hence there is no current in the outer half of the © 


N 


90 ELECTRICAITGH TING. 


wire. The currents from // and / return to the dynamo D by the 
— conductor as shown. In a similar manner the flow of current 
in any multiple-wire system may be determined, no matter how 
large or how small the loads on the different parts may be. 

The next step is to determine the voltage at the various points, 
as indicated in Figs. 66 and 67. Let us first consider the case 
(Fig. 66) of 10 amperes being required at 4, with no current used 
in the rest of the system. Assuming each conductor to have one 
ohm resistance, the drop on the + is 10 volts, and the same on the 
® wire, so that the lamps receive only 95 volts, the pressure at 
the dynamo being 115 volts. There will be no drop on any of the 
other three wires, since no current is drawn from them. It is 
interesting to observe that the potential difference between the 
extremities of the ® and © wires will be 125 volts, as shown in 


10 VOLTS DROP 














+ 10 VOLTS DROP E + E 
'415|VOLTS 95] VOLTS 115) VOLTS tool VOLTS 
: No DROP 5 VOLTS DROP 
® © 
125) VOLTS 4islvoLTs 1125\VOLTS  120)VOLTS 


2.6 VOLTS DROP [2.5 VOLTS pRop 


5 VOL 
=) NO DROP =) TS DROP NO DROP 


115] VOLTS 
115|VOLTS 415, VOLTS 107.5|VOLTS  105|VOLTS 







415]VOLTS 
NO DROP a 
J 


Figs. 66 and 67. Distribution of Potential in Five-Wire Systems. 


Fig. 66. If three other groups of lamps were added, so that 10 
amperes would flow directly across from £ to /, the total drop 
would be 20 volts as before, 10 volts drop being transferred from 
the @ to the — wire, and each group would receive 110 volts in- 
stead of 95, the aggregate number of lamps being four times as 
great. This brings out forcibly the advantage of a perfectly bal- 
anced five-wire system over a two-wire circuit, four times as many 
lamps being supplied with one-quarter as much drop for each. 
With groups of lamps placed at £, 7, G, H, and / (Fig. 67 
corresponding to Fig. 65), the pressure is far from uniform, al- 
though the system is fairly well balanced in the number of lamps, 
but not in their position. This potential diagram is made by draw- 
ing from the five points marked +, @, O, ©, and —, lines repre- 
senting the pressure in the respective conductors and portions 


THREE AND FIVE WIRE SYSTEMS OF DISTRIBUTION. Q1 


thereof. By comparing Figs. 65 and 67 it will be seen that the 
direction of these lines is easily and definitely determined, the drop 
or slope of each section being equal to its resistance multiplied by 
the current flowing in it. In this connection it should be noted 
that the current in each group of lamps has been assumed to be 
constant, but it is evident that the group at _/, receiving only 105 
volts, will take less current than those at G, where the pressure is 
117.5 volts. This fact might be allowed for by modifying the val- 
ues of the current in proportion to the voltage; but the resistance 
of the lamps also varies, so that it would be very difficult to calcu- 
late the current that each group would take. In practice conduc- 
tors are designed to supply a given current at a certain point ; and 
slight variations in current due to changes in resistance, working 
conditions, etc., are not usually considered. 

This may appear to be a somewhat rough method, but is not 
only justifiable, but practically unavoidable. In electric railway 
work, for example, the current required by a car varies greatly with 
the speed, grade, condition of track, load on the car, etc. Hence 
the only practicable plan is to assume a certain average current, or 
a certain maximum current, in designing the generating plant, con- 
ductors, etc. The average current corresponds to the ordinary 
working conditions, and the maximum current to the greatest pos- 
sible requirements. The same is true for electric lighting, in 
which variations in the resistance of lamps are far less important 
than the changes in the number of lamps which are continually 
being made. 

In practice the electric-light engineer considers the zzzézal 
voltage at the generators, the reszstance and current in each portion 
of the conductors which gives the d@vof, the latter subtracted from 
the initial voltage gives the pressure at the lamps. It would be an 
easy matter to calculate the resistance of the lamps by dividing the 
pressure they receive by the current flowing through them ; but as 
a matter of fact one rarely, if ever, does this. It is only the inex- 
perienced student who attempts to apply Ohm’s law to the circuit 
as a whole. The practicing engineer confines it to determining 
the drop on the conductors, and usually considers one portion at a 
time, the drop in each being equal to its resistance multiplied by 
the current carried by it. The same is true in power transmission 
and distribution, including electric railway work. In fact it is 


92 ELECTRIC. LIGHTING: 


practically impossible to predetermine the resistance of the whole 
circuit except in very simple cases. 

The author has examined five-wire systems in successful opera- 
tion on a large scale in Paris and in Manchester, England. The 
difficulties encountered are not serious, and are apparently not 
much greater than with three-wire plants. Nevertheless, the in- 
_ creased number of conductors does involve more complication and 
possibility of accident. In the future the three-wire 440-volt sys- 
tem will undoubtedly be selected in preference to five-wire system. 

Seven-wire System. — This is the next higher multiple-wire 
system that would be used, since it can readily be divided into two. 
four-wire systems, or three three-wire systems, in order to supply 
current to individual buildings where it is not necessary to carry 
all seven conductors. Neither the four-wire nor the six-wire sys- 
tems are capable of being conveniently divided into equal parts in 
this way ; hence they are not to be recommended for adoption, ex- 
cept perhaps in some special case. The seven-wire system, with 
all conductors of the same size, requires 0.0972, or a little less. 
than one-tenth as much copper as an equivalent two-wire circuit ; 
but its complication is so great as to make it of very questionable 
desirability. Its design and operation would be similar to that of 
the three- and five-wire systems already described. 


DIRECT CURRENT TRANSFORMER SYSTEMS. 93 


Creer Ea 


DIRECT CURRENT TRANSFORMER SYSTEMS OF ELECTRICAL 
DISTRIBUTION. 


Tue fact that electrical energy can be readily transformed 
from a higher to a lower voltage, or vice versa, constitutes one of 
its most important advantages, and enables it to be conveniently 
and economically transmitted and distributed. The most promi- 
nent example of this method is the ordinary alternating current 
system, in which a high pressure of a thousand volts or more, gen- 
erated by the dynamos, may be carried by small wires to a consid- 
erable distance, and there transformed to a low voltage that is 
harmless to persons and adapted to supply lamps, ete. 

The direct current can also be transmitted in a similar manner, 
but it requires rotary machines instead of the simple induction 
coils or “static’’ transformers that are used for the alternating 
current. 

Rotary transformers consist of a motor and a dynamo combined, 
the former being driven by the current from the main or primary 
circuit, and the latter generating the current for the sccondary cuir- 
cuit, by which the lamps, etc., are supplied. It 1s obvious that the 
dynamo may be designed to produce any desired voltage without 
regard to that of the primary circuit. But in every case the watts 
— product of the volts and amperes —are less in the secondary cir- 
cuit by an amount corresponding to the frictional and other losses 
which necessarily occur. This device has been given many names, 
such as dynamotor, motor-dynamo, motor-transformer, rotary-trans- 
former, motor-converter, and rotary converter. The first of these 
has the advantage of being a single word, but has been objected to 
because the order in which the two machines work is inverted. 
This is not a serious objection, and the term is often used, being 
particularly appropriate to the construction in which the motor 
and dynamo are incorporated as one machine. In contradistinction 
the name motor-dynamo may be applied when there is a combina- 


94 ZLECTRICHUGHTIING 


7 


tion of two machines. The word transformer has been almost unt 
versally adopted for the induction coil or static transformer, so that 
the term converter, which was formerly applied to this device, is 
now free to be used for the machine in which alternating are 
changed into direct currents, or vice versa, in the same armature 
winding as shown in Fig. 71. 

In dynamotors the two armature windings are placed upon 
the same core and are acted upon by the same field magnet, as 
illustrated in Fig. 68. This construction secures compactness, and 
also causes the armature reaction of the dynamo to practically 





Fiz. 68. Dynamotor, with Single Field. 


neutralize that of the motor, thereby avoiding sparking and other 
troubles. But it is open to the objection that it is somewhat diffi- 
cult to insulate the two windings from each other, and absolutely 
prevent the high voltage of one from breaking through to the 
other. Therefore this arrangement is not desirable where there 
are great differences in potential between the primary and second- 
ary circuits, unless special precautions are taken. Another lim- 
itation of this construction is the difficulty of acting on the two 
armature windings independently for purposes of regulation. Since 
both are wound upon the same core and are under the influence of 
the same field, it is hardly possible to change the speed, magnetic 


DIKECIMCORRENT TRANSHORMER SVSTEMS. 95 


flux, or other conditions of one with respect to the other. In other 
words, the ratio of conversion, that is, the relation between the 
primary and secondary voltages, is practically constant, no matter 
how much the speed or flux may be varied. To be sure the differ- 
ence of potential between the secondary brushes may be decreased 
by introducing resistance in the primary circuit, but this merely 
has the effect of reducing the available voltage supplied to the 
motor. The amount of this reduction is the drop =/A, in which 
/ is the primary current and & the resistance inserted. A corre- 
sponding decrease in voltage is produced in the secondary circuit, 
but the ratio of conversion as measured at the brushes remains 
substantially unchanged. Resistance put in the secondary circuit 
will have a similar effect in Set the available potential, but 
in either case the loss of energy 
is considerable, its value in watts 
being /?R. The so-called “reg- 
ulation” is also seriously inter- 
fered with; that is, the available 
secondary voltage varies greatly 
with changes in the load, be- 
cause any alteration in the cur- 
rent has a corresponding effect 
onthe dropel As eouch a Vari- 
ation in pressure would usually 
be very objectionable; in electric lighting, for example, the voltage 
would fall as more lamps were added in parallel. 

In order to secure independence of action between the motor 





ir eae amet 


Fig. ud. WMotor-Dynamo. 


and dynamo portions of a rotary transformer, the two armature 
windings should be carried by separate cores, each .being acted 
upon by its own field magnet. This allows the field of the dynamo 
to be independently regulated, in order to vary the voltage gener- 
ated. In fact, any of the well-known methods of dynamo regula- 
tion may be employed. For example, compound or over-compound 
winding applied to the dynamo field will give a constant or a rising 
pressure, with increase of current in the secondary circuit. In 
these cases the separate armatures may be mounted upon the same 
shaft, with only one pair of bearings, in the form shown in Fig. 
69, or the two machines may be arranged upon the same base with 
an intermediate bearing, as represented in Fig. 70. If desired two 


96 ELECTRIC LIGHTING. 


- 


entirely distinct machines may be belted or directly coupled to- 
gether. In fact, almost any motor and dynamo may be employed 
in this way, provided the former has sufficient power to drive the 
latter, and the mechanical connection is arranged to give the proper 
speeds. . 

It is evident that the motor of a rotary transformer may be 
designed to operate with an alternating current, and the dynamo 
to generate a direct current, or vice versa, in order to convert alter- 
nating to direct currents, or the converse. 





Fig. 70. Motor-Dynamo. 


Still another type is the rotary converter, in which the same 
armature winding performs both the motor and dynamo functions. 
A simple form of this machine, shown in Fig. 71, consists of a ring 
armature, diametrically opposite points of the winding being re- 
spectively connected to two collecting rings. When the armature 
is supplied with direct current in the usual way by the brushes + 
and —, it will revolve as a motor, and an alternating current may 
be obtained from the bruskes A and 4. This action can be easily 


DIRECT CURRENT TRANSFORMER SYSTEMS. oF 


understood when it is considered that, at the time indicated, the 
outer collecting ring is connected to the top or + point of the 
winding, and the inner ring to the bottom or — point of the wind- 
ine wehence thescurrentstends toy flow from) the» brush 67 to’ the 
brush 4; but when the armature has turned through 180 degrees, 
or half a revolution, these conditions will be exactly reversed, and 
the current tends to flow from A to &. Thus it is seen that an 
armature having only a single winding may be fed with a direct 
current, and will give out an alternating current. The ratio be- 
tween the primary and secondary voltages is practically fixed in 
this form of converter, since the maximum value of the alterna- 
ting £.4/.F. is equal to the voltage of the direct current, as is evi- 
dent from the diagram. With a true sine wave the effective value 
of the alternating Z.I7F-. is 0.707 of the maximum L.IZF- 

If these machines are used 
to convert alternating to direct 
current, they are run as syn- 
chronous motors; hence they 
must first be brought up in 
speed by some extraneous 
power, or by operating them 
as direct current motors, until 
they are in synchronism with 
Poemaluctnating current ‘by © Fig. 77. Alternating-Direct Current Converter. 
which they are to be operated. 

These machines are capable of exciting their own field magnets 
by the direct current which they generate. 

By tapping the direct current winding at three or four points, 
machines are made for generating or utilizing three- or two-phase 





alternating currents respectively. 

The actions of these machines are brought out in a paper by 
Professor R. B. Owens, and in the discussion which followed.* 

Direct Current Transformer Systems of Distribution. — The 
usual arrangement of rotary transformers in electrical distribution 
is that represented in Fig. 72, being analogous to the ordinary 
alternating current system with static transformers. The current 
produced by the main generator G is carried to the machines by 
the conductors A and 4, to which the motor portions 7 of the 


* Trans. Amer. Inst. Elec. Eeng., July, 1897. 


98 ELEGTRIC LIGHTING: 


rotary transformers are connected in parallel. These motors are 
provided with shunt wound field coils that may be connected to the 
primary or to the secondary circuit, consequently the machines run 
at a practically constant speed. The dynamo portion D of the 
transformers are connected to the secondary circuits which supply 
the lamps, etc., £, as indicated. The field magnets of these dyna- 
mos may also be fed by the main circuit AZ, or they may be self- 
excited by shunt or compound winding. 

This system has the following advantages and disadvantages 
compared with the alternating current system. Rotary transform- 
ers are more complicated, cost more, require more attention, and 
are less efficient than static transformers. But it has been shown 
that they may be compound or over-compound wound, in order to 
supply a uniform or rising voltage, which is not practicable with 
static transformers. Furthermore, it is generally found that rotary 





Fig. 72. Distribution by Rotary Transformers in Parallel. 


transformers are easily taken care of, and rarely get out of order. 
In many cases their use may be desirable or necessary, as, for ex- 
ample, in electrolytic, chemical, or metallurgical work, in arc light- 
ing, in connection with storage batteries, or for other purposes for 
which direct currents are converted from alternating, or vice versa. 

Rotary transformers may also be arranged as illustrated in Fig. 
738, the motor parts being all connected in series with the main 
generator G, and the dynamo elements J of the transformers being 
connectedito the lamps, \ete.;22. ti the “current, isskepe constant 
(the generator G having a regulator like a series arc dynamo), 
and the motors J/ are simple series-wound machines, they will 
exert a certain torque, or turning effort, which will be constant. It 
follows, therefore, if the dynamos J are also series wound, that 
each will generate a certain current which will be constant. If 
lamps or other devices designed for that particular current are con- 
nected in series on the secondary circuits, the dynamos D will 
always maintain that current, no matter how many lamps there 


DIRECT CURRENT TRANSFORMER SYSTEMS. 99 


may be. When lamps are added, the resistance of the local circuit 
is raised, and the current in it decreases, so that the dynamo in- 
creases its speed until it generates sufficient 4.477. to produce 
practically the same current as before. Hence this constitutes a 
system which is self-regulating, when lamps, etc., are cut in or out 
of the secondary circuits. No harm results even when the second- 
ary is short-circuited, since only the normal current can be gene- 
rated. But if the secondary circuit is opened, then the machine 
will race, and probably injure itself by centrifugal force, because 
the torque of the motor J7/ has its full value, and there is no load 
upon the dynamo DY. To guard against this danger, some auto- 
matic device should be provided to short-circuit the field or arma- 
ture of the motor when its speed or counter £.4/./. rises above 





Fig. 73. Distribution by Rotary Transformers in Series. 


a certain point. Another way to operate such a system would be 
to use motors /, with governors that maintain a constant speed 
for all loads, in which case the dynamos PY should be shunt or 
compound wound, to feed lamps, etc., in parallel at constant 
potential. 

Motor Dynamos as ‘ Boosters’’ and Compensators. — The-.ma- 
chines described in the present chapter for use in converting direct 
currents from one voltage to another are also applicable as “ boos- 
ters” in feeder regulation, and as compensators in three- and five- 
wire systems of distribution. The motor-dynamo illustrated in 
Fig. 70 is well adapted to being employed as a “booster” in Fig. 
39, for example. The left-hand machine could be driven as a 
shunt-wound motor by current obtained from the main generator 
D (Fig. 39), and the right-hand machine (Fig. 70) would serve as 
the “booster” R or S to raise the voltage in the feeders A or B 
(Fig. 39). The double machine shown in Fig. 70 or in Fig. 68 


100 ELECTRIC LIGHTING. 


- 


could also be used as a compensator to subdivide the total voltage 
in the three-wire system indicated in Fig. 56. Indeed, it is cus- 
tomary to use motor-dynamos for these purposes. 

The Oxford System. — One of the most prominent examples 
of transmission and distribution by means of high-tension direct 
currents is the plant that has been in operation at Oxford, Eng- 
land, for several years. Similar systems are also used in London 
(Chelsea), Shoreditch, and other places in Great Britain, the name 
“Oxford System ”’ being applied generally to this class of installa- 
tions. They may be regarded as extensions of the simple arrange- 
ment shown in Fig. 72. 

In the diagram, Fig. 74, which represents such a system, D D 
are the main generators supplying direct currents at 1,000 or 2,000 





+ 


eS a 
Od 











Fig. 74. High-Tension Direct-Current System. 


volts to the high-tension *bus bars H H. Their field coils /F are 
fed from the low-tension ’bus bars / Z, that receive current at 100 
or 200 volts from the secondary circuit of the motor-dynamo K, the 
primary Z of which is supplied from the high-tension ’bus bars 
ff H{ by the wires W. The storage battery B is also connected to 
the low-tension ’bus bars Z, being charged by the machine 4, in 
order to give current for lighting the station when all the genera- 
tors (D PD) are stopped, and also for exciting their field magnets in 
starting them.: The current is carried from the high-tension "bus 
bars in the generating plant over transmission conductors JZ to the 
two ‘bus bars at the distributing station, that may be placed at a 


DIRECT-CURRENT TRANSFORMER SYSTEMS. AGL: 


considerable distance without involving large expenditure for the 
conductors, since the energy is transmitted at high voltage. From 
these ’bus bars, the high-tension current is conveyed by the pairs 
of feeders / / to the primary circuits of the motor-dynamos Y 
(located at sub-stations), the secondary circuits of which connect 
with the three-wire mains J7 7 17, supplying the outside wires at 
about 200. volts. 

The lamps /// are fed from these three-wire mains in the usual 
manner. The motor-dynamos Q at the various sub-stations may 
either be controlled by attendants at the sub-stations, or they may 
be started and stepped from the distributing station by means of 
the starting rheostat S placed in each feeder circuit. In the latter 
case, the motor-dynamos are provided with series field coils 7 in 
order to give magnetization for starting up, after which excitation 
is produced by a shunt winding (not shown) supplied from the 
secondary circuit. The latter is connected to or disconnected 
from the mains 7 by the switch C, that may be operated from the 
station by means of the magnet XY and wires P. The latter also 
serve as pressure wires, the voltage on the mains being indicated 
in the station by a voltmeter V. 

Compensators U are connected to the three-wire mains J7/ at 
various points to equalize the voltage on the two sides of the sys- 
tem. These machines may be simple, like 17 V in Fig. 56, or they 
may be provided with series winding, as in Fig. 58, in order to 
raise the pressure on the more heavily loaded side when the sys- 
tem becomes unbalanced. The storage battery G is connected to 
the mains 7 for the purpose of supplying current during the day, 
or when the load is light, thus enabling all of the main generators 
D D,and motor-dynamos Q Q, to be stopped a considerable portion 
of the time. This battery is charged when the generating plant is 
running, the increased voltage required being produced by the 
booster 7, or a differential booster may be used for the purpose. 

If desired, the storage battery G may be employed to supply 
current for the “peak” of the load-curve (i.e., the short period of 
maximum load), thereby relieving the generating plant, the feeders 
FF, and the motor-dynamos Q Q, at the time of heaviest load. The 
battery may be charged when the load is lighter, so that this plan 
of working would tend to secure a uniform load on the machinery 
while running, and would also allow it to be stopped when the 


102 ELECTRICAIIGEHILING. 


load is very light. Storage batteries may be installed in the gen- 
erating plant (as at 4), in the distributing station, in sub-stations 
on the mains (as at G), or in all three places; the nearer they are 
to the lamps, the more of the apparatus and conductors they may 
relieve at times of maximum load. In fact, one of the advantages 
of this or other direct-current system is the ability to use storage 
batteries in connection with it. In some cases the distributing 
station may be omitted, the feeders // being run directly from 
the ‘bus bars in the generating station to the motor-dynamos 
Q in the sub-stations. The Lvectrical World (N. Y.) of March 12, 
1898, contains a description of this system as used on a large scale 
at Chelsea, England, also the variable ratio direct-current trans- 
formers that are employed there. A description and illustrations 
of a more recent installation of this character at Bromley, England, 
are given in the Electrical World and Engineer (N. Y.) of Feb. 17, 
and in the London Evectrician of January, 1900. 

An important method of electrical distribution consists in trans- 
mitting the electrical energy by means of alternating currents, 
usually two- or three-phase, from the generating plant to stations 
at which it is transformed into direct currents by means of rotary 
converters, and distributed for highting and other purposes. Such 
systems will be described after the principles of alternating cur- 
rents have been considered. 


NETWORKS OF ELECTRICAL CONDUCTORS. 103 


GEITAtP We Reavy: I 
NETWORKS OF ELECTRICAL CONDUCTORS. 


THE most complete system of parallel distribution is that in 
which the conductors are interconnected to form a network. This 
arrangement was developed from the “feeder and main” method 
of Edison,* and is also due to him. It is used in most of the large 
systems throughout the world for low-tension, direct-current distri- 
bution, and is often employed for the secondary circuits of alternat- 
ing-current transformers, especially where the system is a large or 
important one. The enormous networks of mains constructed by 
the Edison Electric Illuminating Companies in New York, Chicago, 
Philadelphia, Brooklyn, Boston, and other large cities, may be cited 
as very prominent examples. Networks are sometimes adopted in 
the interior wiring of buildings ; but they are usually quite simple 
in such cases, being seldom developed much beyond the ring mains 
represented in Figs. 19 and 20, which may be regarded as the 
simplest form of network. 

A two-wire network of conductors is indicated in Fig. 75, 
ABCD being composed of two sets of positive mains at right angles 

to each other, and connected at the points where they intersect ; 

fi FG Hf being a similar network of negative mains represented by 
dotted lines. The mains are supplied with current from the gen- 
erating station S by feeders which are not shown in Fig. 75, 
because they would confuse the diagram. At any desired point a 
lamp will be fed with current if connected between the + and — 
networks. In fact, the case may be considered as equivalent to 
that in which two parallel sheets of copper are respectively con- 
nected to the terminals of a source of electrical energy, lamps being 
connected across from one sheet to the other. 

Distribution of Current and Drop in Voltage in Networks. — In 
order to study the flow of current, let us consider by itself one- 


* See page 30. 


104 MLE CL RIGILALG A LL Er. 


quarter of the positive network, and suppose it to be supplied at the 
point / by a feeder from the station S, as represented in Fig. 76. 
Assuming that the portions of the three horizontal and the three > 
vertical mains included between the points A Y X and Z are uni- 
formly loaded, and not considering the effect of any load outside of 
this region, it follows that one-quarter of the current will flow out 
from the feeding-point / on each of the four mains leading there- 
from. If ten lamps, each taking one ampere, are connected to each 
section of the mains, the initial current in the main / a will be 30 
amperes, since three sections (/a,@ A, and a Y) must be supplied 
by it. When the current reaches the point a, it will have been 
reduced to 20 amperes, since 10 amperes are consumed in the sec- 








ae rts 
| | : 








Fig. 75. Two-Wire Network for Parallel Distribution. 


tion 7a. Hence the average current between / and a is 26 am- 
peres ; and if the resistance for each section be taken as .04 ohm, 
the drop will be 1 volt. The initial current from a to 4 is 10 am- 
peres, and its final value is zero; hence it averages 5 amperes, and 
the drop is .2 volts for that portion. The same is true of the sec- 
tion a Y, provided that the load beyond Y be ignored, as already 
stated. Having thus determined the drop in voltage on the posi- 
tive mains, it is evident that precisely the same drop will also occur 
on the negative conductors. A lamp at_/ will receive the full pres- 
sure supplied by the feeder, which may be assumed to be 112 volts ; 
a lamp at a will have 112 — (1 + 1) = 110 volts; and a lamp at 4 
will be sféd* with 112-— ‘(1 4-1 4592 282) = 109.6) volts™ sSimilar 
statements apply to the lamps at the other points, W Z, etc. 


NEDTWORRSRGL LLEOTRICAL, CONDUCTORS: 105 


When the lamps are not equally distributed, the problem is 
much more difficult to solve. In the apparently simple case of a 
single lamp connected at W, a large portion of its current will 
flow directly from / to W, but a considerable fraction of it will 
take the path / a Y W, and also the path /zZ W. Since there is 
a flow of current from /to A, the latter must be of lower potential 
than the former; hence a small amount of current will take the 
course /7 A Y, and if the network were extended beyond 4, some 
current would follow still more indirect routes. Current would 
also pass through the remainder of the network shown in Fig. 75, 
as well as through the portion represented in Fig. 76; in fact, a 
single lamp connected at any point of a network would cause cur- 
rent to flow in every section except a few that might happen to 
have no potential difference 
between their ends. With a 
number of lamps irregularly 
located, the conditions  be- 
come even more complex. 

It might be supposed that 
a solution of the problem 
could be obtained by compar: 
ing the resistances of the va- 





Fig. 76. Portion of Network Represented 
in Fig. 75. 


rious paths. For example, 
the course /a Y W has three 
times the resistance of / W, hence the current in the former should 
be one-third as much as in the latter. But this is not true, because 
Jj A aqis in parallel with / a. If we attempt to allow for this by 
calculating the joint resistance, the case is further complicated by 
the fact that the section /7 carries current that flows vza X as 
well as through A, and so on. A correct method would consist 
in applying Kirchhoff’s Laws, which are as follows : 


1. The algebraic sum of the currents in all the conductors that meet 
at any point ts Zero. 

2. The algebraic sum of all the products of the currents and resis- 
tances in conductors forming a closed loop equals the algebraic 


sum of all the E.M. Fs in the loop. 


In the networks under consideration there is usually no E.M.F. 
working within each loop, as, for example, the loop /a Y W; 
therefore we may simplify the second law as follows: 


106 ELECTRIC LIGHTING. 


- 


The algebraic sum of all the products of the currents and resistances 
in conductors forming a closed loop ts zero. 


The application of these principles to simple cases has already 
been given on pages 35 and 49; but it would be difficult to apply 
them to the extensive and complicated networks used in practice, 
particularly when the lamps are unequally distributed. Neverthe- 
less, methods for making such calculations have been given by 
Herzog and Stark,* Herzog,+ Coltri,t Muellendorff,§ and others. 

Electrical Model of Network. — In the pioneer work of Edison 
in 1882, the designing of the underground network of conductors 
was aided by constructing models in which the conductors were 
represented in miniature by copper wires. If the model is correct 
in scale, it is possible to determine from it the distribution of cur- 
rent and drop with various amounts and positions of load. This 
plan can be followed in any case, but would ordinarily be consid- 
ered too much trouble, although it might often effect a considerable 
saving in, or better arrangement of, the copper. | 

Mechanical Model of Network. — Another method of solving 
this problem was devised by H. Helberger || of Munich, and con- 
sists in employing a mechanical model in which the conductors are 
represented in length and position by horizontal strings stretched 
with a certain force corresponding to the cross-section of the con- 
ductor, the load being applied in the form of weights that are hung > 
upon the strings, and are proportional to the current consumed at 
the various points. The amount that the strings are depressed 
indicates the drop in voltage, being usually limited to a certain 
value in a given case. The points at which the strings are sup- 
ported correspond to the feeding-points, being raised or lowered 
with respect to each other a distance proportional to the difference 
in the electrical pressures with which they are fed. 

Actual Design of Network. — These methods for determining 
the size of the mains in a network are not much used in America, 
although they are applied quite generally in Germany. Experience 


* Llektrotechnische Zeitschrift, 1890, p. 221, and Electrical World, vol. xv., p. 300. 

+ Llektrotechnische Zeitschrift, 1893, p. 10. 

t Zdzd., 1893, p. 425. 

§ Zbid., 1894, pp. 67 and 236. 

|| German Patent No. 68918, Class 21, April 5, 1892. See also Western Elec- 
trician, April 27, 1897. : 


NETWORKS OF ELECTRICAL CONDUCTORS. 107 


in this country has shown that it is sufficient to employ a few stan- 
dard sizes of mains. In New York City, for example, each of the 
three-wire mains has a cross-section of 350,000 circular mils in 
the central and heavily loaded portions of the network, and a cross- 
section of 200,000 circular mils in the outlying or less heavily 
loaded districts, and in some cases conductors of 150,000 circular 
mils are large enough. It is not found necessary to specially 
determine the size of each individual main or section thereof ; the 
same size being used throughout a large district, and having been 
selected with reference to the general rather than local conditions. 

The justification for this apparently crude practice is, first, the 
simplicity of laying and maintaining a network composed of only 
two or three standard sizes of mains, larger or smaller sizes being 
either too clumsy or too weak mechanically ; second, it is prac- 
tically impossible to predetermine the current that a main will 
carry, the demand upon it being often much greater or less than 
was expected; third, an excess of copper in one portion of a 
network tends to help other portions that are more heavily loaded, 
and conversely a small section of main acts as a weak link in the 
chain. 7 

It is important to appreciate this interdependence of the parts 
of a network of conductors, as it constitutes its chief advantage. 
In the mechanical model already referred to, it is evident that all 
of the strings would aid each other in supporting a weight hung at 
any point upon them. The electrical analogue acts in a similar 
manner. 

As already stated, it is customary to construct networks with 
certain sizes of mains which have been found by experience to be 
suitable for towns having a certain density of population, character 
of service, etc. In cases where this very empirical method cannot 
be followed, or when it is desired to check it by calculation, a care- 
ful plan of the given district should be made, and lines representing 
the proposed mains are then drawn. A main (2- or 3-wire as the 
case may be) is run through each street, or two mains may be 
laid, one on each side, in: order to reduce the trouble of making 
house connections. In the case of unimportant streets in which 
there are no customers, the mains may be omitted or put in later. 
Where the mains intersect they are connected, all the + conduc- 
tors (of which there are usually four or eight) being brought to- 


108 ELECTRIC LIGHTING 


-* 


gether, the same for the — conductors, and also for the + conduc- 
tors in a three-wire system. The connection of four + wires and 
four — wires in a two-wire system is represented at /and JW in 
Fig. 75. Having thus laid out the entire network, certain feeding- 
points are then chosen. ‘There is no absolute rule for determining 
their position, but they should be located to give as nearly uniform 
voltage as possible throughout the system. They should be ar- 
ranged so that the feeders can be run conveniently to them and 
connected to the network, and should be nearer together where the 
load is great, and wzce versa. In case it is subsequently found that 
they are too far apart, others may be added without disturbing the 
feeders and mains already laid. In this way increase of load upon 
the system may be provided for at any time. It is also possible 
to reénforce the mains by laying others parallel to them, but prac- 
tically the same result is obtained when additional feeders are put 
in. If, for example, the average distance between feeding-points 
is reduced to one-half, the average current on a given main will also 
be one-half as great as before, and since it flows only one-half as 
far, the drop would be one-quarter as much. Extending a network 
of mains in any direction will also tend to help the conductors 
already laid, because it provides more paths for the current, as 
explained on page 104. 

The Edison system of underground conductors originally 
adopted for network distribution and still very generally employed 
for the purpose will be described in the chapter on Underground 
Conductors. Other methods of constructing such networks will 
be given under the same heading. 


PRINCIPLES OF ALTERNATING CURRENTS. 109 


CHAPTE.REAViT: 


PRINCIPLES OF ALTERNATING CURRENTS. 


Introduction. -— The various principles and facts concerning 
direct current distribution set forth in the preceding chapters, ap- 
ply also to alternating current systems. But in addition to the 
simple phenomena due to resistance, which occur in the former 
case, there are certain additional factors that must be considered 
in connection with alternating current transmission. The flow of 
a direct current, which is steady, is entirely determined by the 
ohmic resistance of the various parts of the circuit ; and if all these 
resistances are known the distribution of potential and current can 
be determined exactly. The flow of an alternating current de- 
pends not only upon the resistance, but also upon any ¢tuductance 
(self or mutual inductance) or capaczty that may be contained in or 
connected with the circuit. These two factors have absolutely no 
effect upon a direct current after a steady flow has been estab- 
lished, which usually requires only a small fraction of a second. 
But in an alternating circuit either or both of them may be far 
‘more important than resistance, and in some cases may entirely 
control the action of ‘the current, the effect of resistance being 
insignificant. 

Since alternating current problems involve a consideration of 
three factors, they are usually more complicated and difficult to 
solve than those relating to direct currents. Nevertheless, by an 
extension of the principles and methods already explained, it will 
be found that alternating current systems can be designed correctly 
and without great difficulty. 

Practically the only reason for employing alternating currents 
in electric lighting is to enable the cost of the conductors to be re- 
duced by using high voltages and transformers. It has already 
been shown that the cross-section of a wire needed to convey a 


110 ELLE CLE GLLIGET UNG. 


given amount of electrical energy in watts, with a given percentage 
of “drop” or loss of potential in volts, is inversely proportional to 
the square of the £.47./. employed: hence it requires a wire of 
only one-quarter the cross-section and weight if the initial voltage 
is doubled. The great advantage thus obtained by the use of high 
tension can be realized either by a saving in the weight of wire 
required or by transmitting the current to a greater distance with 
the same weight of copper. In alternating current electric lighting 
the primary £.J7.F. is usually at least 1,000 and often 2,000 to 
10,000 volts. Even at a pressure of 1,000 volts an advantage of 
100 to 1 is gained over a system operating at 100 volts. This 
enormous difference enables a given number of lamps to be sup- 
plied at a far greater distance, and at the same time the conductors 
weigh very much less. ‘These facts make it unnecessary to design 
a system of alternating current conductors with the great care that 
is required for direct current distribution, since the use of. slightly 
larger conductors will make up for any small differences in the 
arrangement of the feeders and mains. The result is that ordinary 
alternating current systems of conductors are less complicated than 
those used for direct currents. The very elaborate network of 
mains, for example, often employed for the latter is seldom required 
for the former except in the low voltage secondary distribution. 

On the other hand, the actual uniformity of voltage secured in 
direct current circuits is usually superior to that obtained on alter- 
nating current systems. This is partly due to the fact just stated, 
that less care is required in designing the circuits, consequently 
there is a tendency to exercise too little care. The difference also 
arises from the effects of inductance and capacity, which produce 
variations in potential as great as, or greater than, those due to re- 
sistance alone. The exact influence of these factors under various 
conditions will be considered later. 

The reason that the alternating current can be used at the high 
pressure of 1,000 volts or more, while the direct current is limited 
to about 110, 220, or 440 volts for constant potential lighting is 
due to the greater facility with which the alternating current can 
be transformed from a higher to a lower pressure, and vce versa. 
This is accomplished by simple transformers, consisting merely of 
two or more coils of wire wound upon an iron core. Since there 
are no moving parts, the attention demanded and the likelihood of 


TAENOIEL BoVOPreALILRINALTING CURRENTS, BLE 


the apparatus getting out of order are small. This enables the al- 
ternating current to be generated at or transformed to a high pres- 
sure suitable for transmission over long distances with small con- 
ductors, the potential being locally transformed to that required by 
the lamps, usually about 100 volts. In order to convert a direct 
current from one potential to another it 1s necessary to employ a 
motor-dynamo, which is practically a combination of a motor and 
a dynamo costing considerably more than an alternating current 
transformer, having a lower efficiency, and being more troublesome 
to take care of. In almost every other respect the direct current 
is preferable for electric lighting; and where the distances are 
not great, as, for example, in isolated plants and central stations 
in thickly populated cities, the direct current has been the system 
most generally and successfully employed. 

Two-phase and three-phase alternating current systems are often 
employed to supply incandescent and arc lights; but they are only 
advantageous for operating motors or rotary converters, and so 
far as lamps are concerned, they are more complicated, and possess 
no compensating superiority over the single-phase system. The 
latter, on the other hand, is not desirable when there are a number 
of motors of anything more than small size, such as fan motors. 
Hence polyphase systems are used in cases where both lamps and 
motors are to be supplied with alternating currents. 

The principles of alternating currents will now be given; but it 
is not intended to treat the subject exhaustively, as there are 
several excellent works entirely devoted to it. It is sufficient 
herein to consider briefly the chief facts, to serve as a basis for 
study and calculations concerning alternating current lines, trans- 
formers, etc. 

Principles of Alternating Currents. — Each armature coil of a 
dynamo tends to generate an £.4/./, which rises to a certain max- 
imum value, then falls to zero, then reverses in direction, and again 
returns to zero. This cycle of changes, which can be represented 
by a curve (Fig. 77), constitutes a complete period ; and since it is 
repeated indefinitely at each revolution of the armature in a bipolar 
field, the currents produced by such an 4£.1/.¥. are called pertodic 
currents. The number of complete periods in one second is called 
the frequency of the pressure, or current. In Fig. 77 the period 
is completed in .01 second, hence the frequency is 100. Since the 


Ly ELECTRICOTAGHIING 


current changes its direction at each half-period, it follows that the 
number of adternations or reversals is twice the frequency. 

Various forms of pressure or current waves may be generated, 
depending upon the arrangement of the armature winding, pole- 





Figs. 78 and 79. Flat-topped and Peaked 
Fig 77. Representation of Alternating E.M.F. Wave Forms. 


pieces, etc. It is possible, by having the pole-faces either consider- 
ably wider or considerably narrower than the armature coils to pro- 
duce a flat-topped wave (Fig. 78); or by making the coils exactly 
the same width as the pole-pieces, a peaked wave (Fig. 79) may be 
obtained. If the lines of force are excessive at the edges of the 
poles, extra waves,-or upper harmonics J] B W, are superimposed 
upon the main or fundamental wave AC (Fig. 80). The extra 


D A E 





ies 4 H 
Fig. 80. Alternating E.M.F. with Third Harmonic. 


wave, /B W, shown is the third harmonic, being always an odd 
number; but in some cases the fifth, seventh, or almost any odd 
harmonic may be present. These harmonics are alternating pres- 
sure or current waves of three, five, seven, etc., times the frequency 
of the fundamental wave AC, which are generated simultaneously 


PRINCIPLES OF ALTERNATING CURRENTS. 113 


with the latter, and modify its form. In the case represented, 
DVEG Fis the wave of £.1/.F. that is actually produced, being 
the combination of the fundamental AC and the third harmonic, 
JBW. For example, the voltage at D is the sum of STZ and /7. 
At V it is the algebraic sum of A and &, and so on. The ideal 





Fig. 81. Sine Curve. 


form of wave generated by a coil of wire revolving about an axis in 
a uniform field is the szve-curve, in which the £.47./. at any point, 
P, is proportional to the sine of the angle 6, through which the coil’ 
has moved (Fig. 81). 

fiethesmaxinune value otuthe: 4:47. /\-at 17 is A. thenithe 
instantaneous value ¢ at any point is 


Cp ieee ea Os (32) 


When the current wave is also a sine-curve, a similar expression 
gives the instantaneous value as follows: 
ham pee ATU (33) 
The sine-wave being the ideal form, practically all calculations 
are based upon it; other forms tend to be converted into the sine 
curve; and it seems to be the best for general use, so it should be 
accepted for the same reason that standard weights and measures, 
screw-threads, etc., are adopted. This is true, even though some 
other form might have advantages for certain purposes. The 
question has been much discussed ; * but the tendency has been for 
_ manufacturers generally to adopt the sine-form, the actual waves of 
pressure and current in most commercial apparatus being close 
approximations to the true sine-curve. 
If all alternating current apparatus is designed for the sine-wave 


* Electrical World, Aug. 4, 1894, p. 107, and many other issues to Dec. 1, 1894. 


114 ELLE CLRICALIG HY ING: 


it is possible to operate dynamos, motors, measuring instruments, 
etc., on any circuit, thus avoiding the endless confusion and difficul- 
ties that would arise if a different form of wave were adopted by 
each manufacturer and for each particular purpose. 

Effective Values of Alternating Pressures and Currents. — 
Since the value of an alternating current is continually varying, it 
is usually more convenient to consider its mean value; but this zs 
not the ordinary arithmetical average. If an alternating current 
is flowing through a conductor, its heating effect at any instant will 
be proportional to the square of the current strength ; and the aver- 
age heating effect for the whole time during which it flows will be 
the average of these squares, —that is, the mean square. It fol- 
lows, therefore, that a direct current, to produce the same heating 
effect, would have a value equal to the square root of this quantity, 


that is, Vmean square. The same is true of alternating current 
2 


E.M.F., since the heating effect is Rs 80 that, with a constant re- 


sistance, the heating is proportional to the square of the voltage. 
The square root of the mean square of the voltage or current is 
called its effectzve value, and is the quantity which is indicated by 
alternating current volt- or ampere-meters. For a sine-wave the 





ee 
effective pressure or current is —= = .707, or about 71 per cent of 


V2 
the maximum value, and conversely, the maximum is V2 = 1.41 
times the effective value, or 41 per cent greater. These relations 
may be summed up as follows: 


Se ers a a 
EE efec = ‘Mean Square of = 50 dine WOT Tee ome: (34) 
St ste oie) AL kA - 
/ efec = */ mean square of 7 biter = 107 Lmaz. (35) 


In practical cases it is usually sufficient to determine the effec- 
tive volts and amperes of alternating currents, the instantaneous 
values being rarely considered except for the purpose of deducing 
formulas, studying phenomena, and other investigations. The term 
virtual is sometimes applied to the Vmean2 values instead of the 
word effective ; but the latter word is now generally adopted. 

Inductance is one of the three fundamental quantities which 
affect the flow of an alternating or other varying current, the other 
two being resistance and capacity. It is due to inductive action 


PRINCIPLES OF ALTERNATING CURRENTS. rls 


ee 


of the circuit on itself, or of one portion of the circuit on another 
portion of the same circuit, in which cases it is called se/f-7nduction ; 
or it may be due to the action of one circuit upon another inde- 
pendent circuit, in which case it is called mutual induction. The 
former is the one generally considered in transmission, and will be 
treated first. 

The unit of inductance, or the “coefficient of self- or mutual in- 
duction,” is called the “exry, which is the inductance of a circuit 
when the £.4/./. induced in it is one volt, while the inducing 
current varies at the rate of one ampere per second. For example, 
if a counter £.A/7.F. of one volt is set. up in a coil when the cur- 
rent is increased at the rate of one ampere per second, then the 
self-inductance of that coil is one henry. 

The physical cause of the phenomenon of self-induction is the 
fact that a current flowing in a conductor tends to produce mag- 
netic lines of force around itself. If the conductor is a helix of 
wire, the lines produced by each turn pass through that turn and 
through most of the others, so that the total flux through the helix 
is large. When the current varies, the lines of force also vary in 
number, and necessarily cut the turns of wire, thereby setting up an 
E.M.F. in the latter. With increasing current this Z.JZF. is 
counter, and opposes the flow ; with decreasing current it aids it ; but 
when the current is steady no £.J/.F. is induced, since the lines 
of force do not vary or cut the conductor. In the case of mutual 
induction, it 1s evident that a second coil & in the neighborhood 
will be cut by the lines of force produced by the first, tending to 
set up an £.M/.F. in £, which will cause a current to flow in it, or 
will oppose or aid a current already flowing, according to the relative 
directions of the lines of force and the current. 

Inductance was defined by the Chicago Electrical Congress of 
1893 in terms of the £.47.F. generated, but it is also proportional 
to the number of turns of wire and to the average flux through 
each when unit current is flowing. This is similar to the first 
definition, since the production of a certain number of lines of force 
by one ampere in one second tends to generate a certain £.1/.F- 

A third definition of inductance may be based upon the electro- 
magnetic energy stored in a coil when a unit current is flowing, 
which energy is proportional to the square of the flux density, 
other things being equal. 


116 ELECTRICOLIGHTIING. 


These three definitions may be summed up as follows: 


Three Definitions of Inductance. — Calling Z the inductance in 
henrys, ¢ and 7 the instantaneous values of the £.1/.F. in volts and 
the current in amperes respectively, z the instantaneous value of 
the average flux through each turn of wire, Z the number of turns, 


LIers ai Tp 
W the energy in joules and oF the time rate of variation of the 
current, we have: 


in terms of £.47.F. 
Ny See (36) 


Sg (37) 


in terms of energy Ne 
W=43Li?, \ (38) 

Reactance due to Self-Induction. — It has been shown that the 
effect of inductance in an alternating current circuit is to oppose 
the flow of current on account of the counter /.J/7.F. which it sets 
up. This opposition may be considered as an apparent resistance, 
and is called reactance to distinguish it from true ohmic resistance. 
The value of the reactance due to inductance is given by the fol- 
lowing expression, in which fis the frequency in periods per second, 
and Z is the inductance measured in henrys 


Reactance = 27fZ. (39) 


The result obtained gives the equivalent or apparent resistance in 
ohms. 


Example.— A coil of wire having a self-inductance of 25 millihenrys = .025 
henry is supplied with an alternating current at a frequency of 100 periods per 
second. Its reactance, assuming its ohmic resistance to be negligible, would be 


2nfL =2 X 3.1416 X 100 X .025 = 15.7 ohms, 
Such a coil would have the same apparent resistance as a non-inductive 
circuit of 15.7 true ohms, and if connected to an alternating current source 


giving 1000 volts at 100 frequency, the effective current flowing through the coil 


[O00 eee 
would be i 63.7 amperes. 


Impedance due to Resistance and Inductance. — Actual circuits 
always have resistance as well as inductance, and in most cases the 
former cannot be neglected. The combined effect of resistance 


PRINCIPLES OF ALTERNATING CURRENTS. 117 


and inductance is called zwpedance to distinguish it from the other 
two, and has the following value in ohms (apparent resistance). 


Impedance = V RK? + (2 2fL)*. | (40) 





Example.—A coil of wire has a resistance of 20 ohms and an inductance 
of .o25 henry. For an alternating current having a frequency of 100 the im- 
pedance of the coil is 





J 2+ (2 rfl)? = Sf 202+ 15.72 = 25.4 ohms. 


Supplied with 1000 volts the coil would receive a current el ee 39.3 


25.4 
amperes. 


The relations expressed analytically in (40) are evidently repre- 
sented graphically by the right- 
angle trianglean Hig. $2, The re- 
sistance A in ohms is laid off on 
‘a convenient scale to form the aS 2Tr¢L 
base, the reactance 2 z/fZ is laid off 
also in ohms to form the perpen- 
dicular, and the impedance in ohms 
is found by-measuring the hypoth- Fig. 82. Graphical Representation. 
enuse of the triangle, since it is 
equal to the square root of the sum of the squares of the other 
two. 

Lag of Current due to Inductance. — Besides opposition or re- 
actance to an alternating current, inductance also causes the latter 
to lag behind the 4.47.7. which produces it. The curve £F in 
Fig. 83 represents the waves of an alternating /£.J7.F. impressed 
upon a circuit containing ohmic resistance without inductance or 
capacity. In such a case the resulting current will reach its maxi- 
mum as well as zero values at the same instants as the A.JZF, 
and may be represented by the curve CD. If now a self-induction 
coil be introduced into the circuit in series with the resistance, the 
current waves will lag with respect to those of E.47.F.; that is, 
the maximum current will flow a little later than the instant of 
maximum £./7.F., as indicated by the dotted curve GH. The 
amount of this lag is measured as an angle called the angle of lag, 
assuming one complete period to correspond to 360°. In Fig. 83 
the current wave is shown as having its zero value one-eighth of a 
period, or 45° behind the zero £.J/.F, and the same for the maxi. 
mum and other corresponding points, hence the angle of lag is 45°. 


118 ELECTRIC LIGHTING. 


The tangent of the angle of lag with a given resistance R and 
inductance Z in the circuit is 


t 2nfL 
ee reactance rf . (40a) 


resistance vs 





Referring to Fig. 82, it is evident that the tangent of the angle ¢ 
is equal to 2xfL +R; therefore ¢ represents the angle of lag, which 
may be easily determined graphically in this way. It is apparent, 
from Fig. 82, that the angle of lag ¢ is small if the resistance is 





Fig. 83. Lag of Alternating Current. 


large compared with the inductance Z, unless the frequency is 
high. It is a fact also, that however large the inductance or fre- 
quency, and however small the resistance, the angle of lag can 
never be greater than a right angle, or 90°. This is evident in 
(40a), since ¢ = 90° when its tangent is infinity. 


Example.— A circuit has a resistance of 2 ohms and an inductance of 
.0016 henry. What is the angle of lag for an alternating current having a 
frequency of 100? 


2nfL = 2 X 3.1416 X 100 X .0016=2 ohms. 


The resistance # is also 2 ohms, therefore tan ¢ = ?=1 and ¢ is 45°. This 
is the condition shown in Fig. 88, the current wave GH (dotted) being 45° be- 
hind the 2.4.7. wave EF. The curve CD represents the current that would 
flow if a wire of 2 ohms resistance without inductance were supplied with 100 
volts alternating “.47./., the current at any instant having one half the nu- 
merical value of the £.4/./. its effective value being 100 + 2=50 amperes with 
no lag. The addition of .0016 henry inductance produces a reactance of 2 
ohms, which combined with the resistance of 1 ohms, makes an impedance of 
J 22 + 22 = 2.82 ohms, which is much less than their arithmetical sum. 

The current is 100 + 2.82 = 35.5 amperes, so that the effect of inductance is 
to diminish the current, and cause it to lag as shown by comparing curves CD 
and G// in Fig. 83. 


PRIVG LEW OLr ALTERVA TING CURKELNIS. 119 


Determination of the Power of an Alternating Current. — Ina 
circuit containing ohmic resistance only, the current wave C does 
not lag with respect to the 4.17.7. wave £, and the power is 
represented by the curve PQ 
in Fig. 84. At any instant 
the power in watts is the 
product of the 4.477. and 
current at that instant, but 
for convenience these values 
(curve PQ) are plotted on 
a smaller scale than & and 
C. The power is positive at 
all times, since the product 
of the positive values of & 
and C’as well as the negative values of D and & are always posi- 
tive, and its effective value is the V mean? of these products, which 
is simply the product of the effective -.47.F., and current, as read 
on a volt and an ampere-meter, that is 





Fig. 84. Power of Alternating Current with no Lag. 


Power =) fee /: Gaels) 


With inductance in the circuit, the current lags behind the 
£.M.F.and the power may be represented by the curve PRQS in 
Fig. 85. The negative values R and S of the power are due to 
the fact that the current C is positive when the -.J7-F. is nega- 
tive, or vice versa ; hence the actual power is reduced, being the 

algebraic sum of these 

a Q quantities. When the re- 

actance is very great com- 
pared with the resistance, 
the current lags 90°; and 
the negative power at 7 
and U, in Fig. 86, is equal 
S to the positive power at P 
and Oso that ‘the actual 
power is zero. _ All that 





Fig. 85. Power of Alternating Current with 45° Lag. A c 
occurs is a charging and 


discharging of electro-magnetic energy in the coil, the amount re- 
turned being nearly equal to that stored. It should be noted that 
the frequency of the power curves in Figs. 85 and 86 is twice that 


120 ELECTRIC. LIGHTING. 


of the £.1/-F. or current. The effective power, when the E.A/.F. 
and current differ in pase — that is, one lags behind the other — is 


Power =Z/cos ¢. (42) 


In this expression 
cos @ is the cosine of 
the angle of lag, and is. 
called the power factor, 
since it is the ratio of 
the veal power to the ap- 
parent power ET. 

To measure alternat- 
ing current power, it is 
necessary to know the 





Fig. 86. Power of Alternating Current with 90° Lag. 


angle of lag if separate 
volt- and ampere-meters are used, or to employ a watt-meter, which 
gives the true reading directly. 


Example. — Taking the same case as before in which the £.47.F. is 100 
volts, the current is 35.5 amperes and the angle of lag is 45°, the real power 
would be 100 X 35.5 X cos 45° = 100 X 35.5 X .71 = 2520 watts, while the ap- 


25) OYE 


parent power is 100 X 35.5 = 3550 watts. 


Capacity is the third quantity which effects the flow of an alter- 
nating or other variable current. This physical quantity is familiar 
in the case of the electrostatic capacity of a Leyden jar or a con- 
denser, and is measured in terms of the favad as a unit, being the 
capacity of a condenser which will contain one coulomb of charge 
at a potential of one volt. Since this unit is much too large for 
ordinary use, the wzcrofarad, or millionth of a farad, is generally 
employed. 

Reactance due to Capacity. — When the two terminals D and 
G of a condenser are connected respectively to the two wires 5D 
of an alternating current source A, as = 
indicated in Fig. 87, the condenser | 
will be charged and discharged continu- OK 
ally, so that current will flow in the Fig. 87. Condenser in Alternating 
wires B and D in spite of the fact that ikea sf th 
the two sides D and G of the condenser are insulated from each 
other, which prevents the actual passage of current through it. 
Thus we see that a condenser is equivalent to a closed circuit 


PRINCIPLES OF ALTERNATING CURRENTS, Peal 


having a certain resistance, or, in other words, it has an apparent 
resistance in ohms which is called its reactance, corresponding to 
that due to inductance. Evidently the flow of current increases 
directly with the capacity and with the frequency, therefore the 
reactance is inversely proportional to these quantities. Calling K 
the capacity in farads, the reactance in ohms is: 


i 
reactance = Daf (43) 
CUITOT tee at, (44) 


Example.— What is the reactance of a 50-microfarad condenser to an alter- 
nating current of 100 frequency? The reactance from (48) is: 
1 1 1 7 
oafk 2X 3.1416 X 100 x .000050 ~ 081416 ~ 21-8 ohms. 





If the Z.A47.F. of the supply is 100 volts, a current of oS = 3.14 amperes would 


flow in the connecting wires. 

Lead of Current due to Capacity. — A condenser is supplied 
with an alternating £.47.F. represented by the curve EF GA in 
Fig. 88. It is evident that current 
will flow into the condenser in one 
direction while the £.1/.F. varies 
from its greatest negative value £& to 
its highest positive value /; and its 
direction is the same as that of the 
positive 4.47. /., therefore, a positive 
wave of current C is produced during 
that time. The condenser is fully charged when the A..F. 
reaches its maximum value F/ so the flow into the condenser 
ceases and the current is zero. The 4.//.F. then falls as shown 
by the line /GH,, and the condenser discharges, producing the: 
negative current wave Y and so on. By comparing the two curves, 
it appears that the maximum current into the condenser occurs 
at a point C, which is 90° ahead of the maximum £.4/7.F. at F, 
and the same for other corresponding points. Hence, the char- 
ging current of a condenser has a /ead with respect to the im- 
pressed #.17.F. The tangent of the angle of lead or negative lag 
is given by an expression analogous to (40a). 





Fig. 88. Lead of Alternating Current. 


Reactance = 2 aK. (45) 
Resistance | R ; 





fal, == — 


12 ELECT RIGALICHIING 


This angle may be determined graphically by a triangle, as in- 
dicated in Fig. 89, similar to Fig. 82; but in this case the reactance 
pode 1 
-=> Impedance due to Resistance, Inductance, and Capacity. 
Gouhes a certain ohmic resistance is in series with a condenser, the 
- impedance or combined apparent resistance in ohms is given by an 
\ expression corresponding to (40). 


is laid off downward, since it produces a lead instead of a lag. 








Impedance = \/e 24 (46) 


if 2 
saa) 
The same result is obtained graphically in Fig. 89. When in- 
ductance and capacity are both present in a circuit, the reactance 
of one tends to balance that of the other, so that the combined 
reactance is the algebraic sum of the two, that is: 
u 
afk (47) 
When all three quantities — resistance, inductance, and capacity 
— are present in a circuit, the combined impedance is 


Reactance = 2 7fZ — 





Impedance = \/ 23+ (2afL — 7K} (48) 
1 
DPE IRS saci 
EE pe ae (49) 


Tangent of angle of lag or lead = R 


The graphical solution is shown in Fig. 90; the inductance re- 
actance being laid off upward, and the capacity reactance down- 





ve 
DEN 
+ 
Fig. 89. Impedance and Lead Fig. 90. Impedance and Lag due to 
Shown Graphically. Three Quantities. 


ward, the difference being the perpendicular of the triangle ct 
which the hypothenuse is the impedance and the angle ¢ is the lag 
or lead, as the case may be. For convenience, the constant 27/ is 
designated as /. 


PRINCIPLES OF ALTERNATING CURRENTS. 123 


Example.—A circuit consists of a coil having 20 ohms resistance and .025 
henry inductance in series with a condenser of 50 microfarad. What is the 
combined impedance and angle of lag when supplied with alternating current 
at a frequency of 100? The impedance from (48) is VY 202+ (15.7 — 81.8)? = 
25.6 ohms, which is less than the capacity reactance (31.8 ohms) alone. The 
tangent of the angle of lead (the capacity reactance being greater than the in- 
ductance reactance) is 





15.7— 381.8 16.1 
2 hoe ieee ON) bi ——_—— .805, 


Power Factor with Resistance, Inductance, and Capacity.—It 
has already been stated (42) that Power = E/ cos ¢, when the cur- 
rent lags on account of inductance. It applies also to a leading 
current in a capacity circuit, and to a circuit containing resistance, 
inductance, and capacity. All that is necessary is to determine the 
angle of lag or lead from (49), or Fig. 90, and the cosine of that 
angle is the power factor. It is evident that the angle of lag, 4, is 
small when the induction and capacity reactances are nearly equal, 
so that they practically neutralize each other, in which case cos 4, 
the power factor, is almost 100 per cent 





1 ; 
Resonance. — If 27/Z = Inf K in (48), then 
1 


and the impedance of the circuit reduces to R simply, just as if 
neither inductance nor capacity was present. In other words, the 
two reactances exactly neutralize each other. The electrostatic 
energy in the condenser discharges when the electromagnetic 
energy in the inductance is being stored up, and vce versa. This 
condition is called electrical vesonance; and the circuit is said to be 
tuned for the particular frequency indicated in (50), since with a 
given £.M/.F., the current will be much stronger for that fre- 
quency than for any other, the impedance being a minimum and 
equal to the resistance only. The 


induction- or capacity-reactance R L K 

may each be very high, in which WS/\/V/0 UII 

case the difference of potential i | S ie U 
Fig. 91. Reactances in Series. 


across either pair of terminals 

will be much greater than the impressed Z.J/.F., since the drop 
in voltage for each part of the circuit is equal to its reactance 
multiplied by the current. This can best be made clear by an 
example. 


124 BLECTRIGQIIGR TING 


Example.— In Fig. 91 a non-inductive resistance 2 of 2 ohms is connected 
in series with a coil Z, having .051 henry inductance (with insignificant resis- 
tance), and with a condenser, A’, of 50 microfarads. What are the conditions 
when 100 volts alternating £.47./. at 100 frequency is applied to the terminals 
Pand U? The impedance from (48) is /2?+ (32. — 31.8)? —/4+ .04 = 2.01 
ohms. This is only .01 ohm, or one-half of one per cent more than the resistance 
alone. With 100 volts the current is 100 + 2.01 = 49.8 amperes. Since the re- 
actance of the coil Z is 32 ohms, the potential difference across its terminals 
and 7 is 32 X 49.8 = 1593.6 volts, and between the terminals Z and U of the 
condenser X it is 31.8 X 49.8 = 1583.6 volts. Each of these is nearly sixteen 
times as great as the impressed voltage at P and UV, which is only 100. This 
multiplication of pressure when resonance happens to occur is sometimes the 
cause of breakdown in the insulation of conductors and apparatus. 

Resonance may be set up by the frequency of the fundamental wave or by 
that of any upper harmonics (Fig. 80). With the fundamental frequency and 
with the third and fifth harmonics present as is often the case, there would be 
three values of the frequency / in (50), any one of which might satisfy the equa- 
tion and give resonance, if the product Z A happened to have a corresponding 
value. 





Circuits Containing Reactances in Series. — Equation (48), or 
the graphical methods shown in Figs. 82, 89, and 90, may be used 
to find the impedance of any combination of resistances, induc- 
tances, or capacities in series. In such a case, the sum of all the 
resistances should be substituted for R, the sum of all the induc- 
tances for Z, and the sum of all the capacities for K in (48). 
These total values may be used also in the diagram represented in 
Fig. 90. The #./.F. is then divided by the total impedance thus 
found in order to obtain the current. The potential difference be- 
tween any two points of the circuit is the product of this current 
and the impedance between those points. The angle of lag is 
found by (49) using total values for Rk, Z, and A. If one or two 
of these quantities are not present in any case, they disappear from 
the equations or graphical representations without affecting those 
quantities remaining. | 

Reactance E.M.F.— In Fig. 92 the horizontal line OA is laid 
off in proportion to the resistance of a certain coil, and the vertical 
line OB is made proportional to its reactance = pl, in which 
p = 2xf. When the, rectangle is completed, the diagonal OD 
represents the impedance = V R2 + (pL)?, being the same as the 
hypothenuse in Fig. 82. Assuming a current of one ampere in the 
coil, the voltage across its terminal is 7 V R?+ (p/)?, which is 
numerically equal to the impedance ; hence the line OD in Fig. 92 








PRINCIPLES OF ALTERNATING CURRENTS. 125 


may be taken to represent that voltage. Similarly the line OA 
gives the drop due to the ohmic resistance, and the line OL shows 
the voltage required to overcome the reactance. That is, the im- 
pressed £.17.F. OD is resolved into two components at right 
angles to each other, one of which, 7/2, overcomes the resistance, 
and the other, g//, overcomes the reactance. The reactance is, 
in fact, an opposing /.4/.F., having an effective value, OF, equal 
but directly opposite to pZ/, and lagging 90° behind the current, 
the phase of the latter being represented by the line OZ. 

These relations, which are very important, may be stated as 
follows: With a given current / the effect of resistance is equiva- 
lent to a counter £.M/./. equal to /R, and represented by the line 
OG. With the same current, the reactance is actually an opposing 
£.MF. having an effective value equal to pZ/, and indicated by 





he oe eee OO 





Fig. 92. Components of E.M.F. 


OF. The combined effect of the two is equivalent to a counter 
E.M.F, equal to OH, which is their resultant. Hence OD, the 
impressed £.47./., must exactly balance O/7; that is, it is equal 
and opposite as shown. The phase of the impressed /.A/.F. is 
represented by the line OD, with respect to which the current 
phase OA has an angle of lag ¢, and OF, the reactance EL. MF, 
has a further lag of 90° behind the current. 

Precisely similar diagrams and reasoning apply to the capacity 
reactance and angle of lead in Fig. 89 and to the combined -induc- 
tance and capacity reactances in Fig. 90. 

Composition and Resolution of E.M.F. and Current. —JIn the 
manner explained above, two or more alternating /.AZ.F’.’s may be 
combined to form a resultant, or one £.47.F. may be resolved 


126 ELECTRIC LIGHTING. 


into two or more components; and the same is true of alternating 
currents. For example, two alternators are running in series, the 
value and phase of the /.J7.F. of one being represented by O17 
in Fig. 98, and the value and relative phase of the other’s F.J/.F. 
being represented by OM. The combined effect is the same as 
that of one 4.477. having the value and phase O/, which is 
the resultant of the two. If OM and OW represent the phase 
and values of two alternating currents, the phase and amount of the 
resultant current are given by OP. This method applies to any 


<M 





Figs. 93 and 94. Components and Resultants of E.M.F. and Current. 


number of £.M.F.’s or currents having any phase angles, the 
various components being combined successively in pairs. Instead 
of constructing a complete parallelogram, it is sufficient to lay off 
OT to represent one /£.4/.F., and 7V to represent the phase and 
value of another £.47.F., then OV is their joint phase and amount. 
In other words, their resultant is the vector sum OV of the two 
vectors OT and 7YV, representing their respective values and - 
phases. 

Impedance of Parallel Circuits.— With two or more simple 
resistances in parallel, the joint conductance is the sum of the sev- 
eral conductances ; hence the joint resistance is the reciprocal of 
the sum of the reciprocals, that is: 


If 





gets ESS | (51) 


In the above, # is the joint resistance of the resistances %, %, 
etc., in parallel. If no inductance or capacity is present, this is 
true of alternating circuits, and always applies to steady direct 
currents. When there is inductance or capacity or both in one 
or more of several alternating circuits in parallel, it becomes neces- 
sary to consider the phases of the currents in the different branches. 


PRAVOIPLEAROLGALIERNATING CORRELNTIS. 127 


Two inductive coils A and & in parallel are assumed to be sup- 
plied with an alternating voltage by the conductors C and JD in 
Fig. 95. To deduce a method for finding their joint impedance, 
let us suppose that OW in Fig. 96 represents the phase and value 
of the current in the coil 4, and OY the phase and value of the 
current in B, then OX gives the phase and value of the resultant 





D . c 1 ie 





Figs. 95 and 96. Impedance of Parallel Circuits. 


current, which actually flows on the supply wires C and D. If 
the effective potential difference between Cand JD is one volt, and 


; Maes 
the impedance of the coil A is /,, then its current OW is —, and 


: ; tin ; 
ieuiesinpedance:ot. 5.15 6/,,,1ts current (CV is Ff The resultant 
ie feoe 
current OX must be ve in which / is the joint impedance of the 
two. The reciprocal of impedance is called admittance ,; therefore, 
the joint admittance of two or more alternating circuits in parallel ts 
the resultant of their several admittances. ‘The equivalent impe- 
dance is found by taking the reciprocal of the joint admittance. 
Many combinations of resistance, inductance, and capacity in series 
and in parallel are calculated out in the work on “ Alternating 
..Currents,” by Professors D. C. and J. P. Jackson, pp. 151-220. 


The following examples are sufficient to show the method : 
Examples.— A non-inductive resistance 7; of 10 ohms is.in parallel with 


an inductive resistance of 10 ohms and .01 henry as indicated in Fig. 97. What 
is the joint impedance and angle of lag for an alternating current having a fre- 





Rz10 L=.0i FR2=10 
Figs. 97, 98, and 99. Inductive and Non-inductive Circuits in Parallel. 


quency of 1272? The impedance of the lower branch may be determined by 
constructing the triangle shown in Fig. 98, in which the base = #2= 10 and the 
perpendicular = 27fZ = 800 =8. Hence, by calculation or by measurement 


128 ELECTRICOLIGHTING 


- 


we find that the impedance, /2= 12.8 and the angle of lag ¢2= 38°40’. In an- 


1 , 5 : : 
other diagram (Fig. 99) the conductance = RI = .100 is laid off horizontally to 


; 1 Le ae 
represent the upper branch, and the admittance = 7, = .078 is laid off atan angle 
2 
go = 38°40’ to represent the lower branch. Completing the parallelogram, it is 
1 ; Me. Yost 
found that the joint admittance = a .168, so that the joint impedance /= 5.95 


ohms, and the resultant angle of lag ¢ = 16°52”. 

In Fig. 100 a coil A1=10 ohms, and Z = .01042 henry is in parallel with a — 
circuit containing a resistance A2= 10 ohms and a condenser having a capacity 
A =150 microfarad, what is the joint impedance and angle of lag @ for an 
alternating current having a frequency of 1273? The impedance of the coil is 
found to be /: = 13 ohms, and the angle of lag ¢; = 39°50! in Fig. 101, and the 
impedance of the condenser circuit is /2=13 ohms, and the angle of lead ¢?= 


R,=10 L=01042 





Rtn 150 
Fig. 100. 





= 38°50f in Fig. 102. The corresponding admittances, each of which is 1+ 13= 
O77, are laid off in Fig. 103 with the same angles of lag and lead. The joint 


; 1 ey as As 
admittance pn 117, so that the joint impedance /=8.47 ohms, and the result- 


ant angle of lag ¢=0, since the lag of one circuit balances the lead of the 
other. At 100 volts the main conductors / and G would supply 100 + 8.47 = 
11.7 amperes. The power factor is 100 per cent (cos ¢=1) so that the true 
power would be 100 X 11.7 =1170 watts. The current in each branch would be 
100 +13=7.7 amperes, one lagging 39°50’, and the other leading 39°50’, with 





Fig. 102, Fig 103. 


respect to the impressed 4.47.7. The fact that the actual current supplied 
(=11.7 amperes) is not equal to the sum of those in the two branches (2 X 7.7= 
15.4 amperes) shows that the discharging of one partly acts to charge the other, 
which is always the case when parallel circuits are not in the same phase. 


Other combinations of resistance, inductance, and capacity may be treated 
in a similar manner. 


ee ? y, v , > 0 9) 
ea PRINCIPLES OF ALTERNATING CURRENTS. 129 


Self-Inductance of Lines and Circuits. — It is possible to calcu- 
late the inductance of coils of wire, but difficult to do so, and in 
most cases it is determined by comparison with standard induc- 
tances. The inductance of aérial lines is easily calculated, since 
they are generally parallel, and the medium has a fixed permeabil- 
ity practically equal to one. Wires laid upon a wall of wood, or 
other non-conducting, non-magnetic substance, or otherwise placed 
out of proximity to such a substance, have practically the same in- 
ductance as aérial lines. 

The following formulas may be used to determine the self- 
inductance of two parallel aérial wires forming part of the same 
circuit, and composed of copper or other non-magnetic matertal. 


A 
Peper centimeter = (5 + 2 log, =| VE (51) 


In this expression / is the self-inductance in henrys per centi- 
meter of each wire, A is the interaxial distance between the two 
wires, and v7 is the radius of each. The dimensions 4 and 7 may 
be expressed in terms of any unit, provided it is the same for both. 
Since the Napierian logarithms in the above equation are 2.302585 
times the common logarithms, and as it is more convenient to use 
the diameter d of the wire instead of its radius, we have without 
appreciable error : 


2A 
Pape cconumMetein= (5 + 4.6 log 7 ae : (52) 
i) per foot = (45, 24 + 140.3 log a 10—-* (53) 


se 
pen mile: = (80.5 + 740. log ) 1) arta) 


For each of two parallel z7oz wires we have the following expres- 
sions, in which the only change is the first constant : | 


2A 
L per centimeter = (75 aloe 7 il eae (00) 


Jf per centimeter = 


2A 
75 + 46 log = jo (56) 


ea 


2A 
L per foot =(2 286 + 140.3 log =) 10- ~9 (57) 
= ie 


L per mile = (12070 + 740 log jo (58) 


a0) ELECTRIC LIGHTING. 


In order to save the trouble of calculating the inductance with 
various sizes of and distances between wires, the following table is 
given: 


INDUCTANCE, IN MILLIHENRYS PER MILE, FOR EACH OF TWO PARALLEL 
COPPER WIRES. 


A.W.G. 
Interaxial No. 0000 000 
Distance. Diam. 
Inches. 0.460 0.4096 
inches. 


0.907 
1.130 
1.260 
1.555 
1.484 
1.576 
1.648 


L019, i 12056 
1.242 | 1.280 
1.372 | 1.410 
1.465 | 1.502 
1.596 | 1.6385 
1.688 | 1.726 
157605 (A 1eto7, 





I~ 





oa eon) 





fp) 
Se 


LOTR RES 
— 


IDE wb 
5 Oo1c GW © 0 
Hon 


C9 rR CO CH Or Orb 


L10t é 1818 | 1.856 
1.799 : scl ih 1.949 
LEST .946 1.982 | 2.023 
1.930 ; 2.042 |. 2.079 
1.971 05: 2.092 | 2.128 
2.023 2. 2.1384 | 2.172 


> e+ Or CO WH 
BG SO Go or 


me Od 
© So 


DNNNRE HEE e ee eee 
on) 


DH HOD MHD. 











interaxial 
Distance. 
Inches. 


1.355 
ieee! 
1.709 
1.801 
1.931 
2.025 
2.097 
2.155 
2248 
2.319 
2.376 
ae DAE AE | 
2.395 .433 2.470 








DWN NWNDNWH HEHE 
OP PR WDE HOD OAG OO 
SCOHTMMOWADWARES 
AIRMAN RHDOaAMD 














LE-xamples.— To show the use of the above formulas and table, let it be 
required to determine the inductance of an overhead line, 13 miles long, con- 
sisting of two No. 0000 copper wires, 48 inches apart. Since it is a metallic 
circuit with two conductors, the total inductance is due to 2 X 1;=3 miles of 
wire. From (54) the inductance per mile is 


( 2 =80.5 + 740 log eS aD ANie 


2) 


PRINGIPEBS ION ALTERNATING CORKENTS. eee 


Substituting, in this expression, the value of the distance between the wires 
A = 48 inches, and the diameter of each wire, a= .46 inch, we have 


6 —6 
L per mile = (80.5 + 740.3 log oy 10. = .001799 henry. 


This is equal to 1.799 millihenry, and is the same value as that given in the first 
column of the table, and shows how those figures were obtained. The total 
inductance of the circuit is 8 X 1.799 = 5.397 millihenrys. 


Impedance of Circuits. — Having obtained the inductance 
of a given line or circuit, by calculation or from the table, the 
reactance from (38) is 2r f Z, and the impedance from (89) is 


VR? + (224fL). The resistance R may be found in the table 
on page 8. Tables are often given showing the impedance of 
jines; but in order to cover the various frequencies, sizes of wire, 
and distance apart, they become too bulky to include in the 
ipresent volume. 

Mutual Inductance of Circuits. — ‘The inductive effect of one 
circuit upon another separate circuit is called mutual inductance, 
‘The most familiar example in electrical engineering is to be found 
in the action between the primary and secondary coils of a trans- 
former, and will be considered later under that head. If two con- 
ductors run parallel to each other, as, for example, two overhead 
jines upon the same poles, an alternating current in one tends to 
induce an alternating 4.A7,F. in the other, the direction of which 
is opposite to that of the inducing current. Consequently two 
parallel alternating currents which are exactly in phase tend to 
oppose each other; but if they differ by 180° in phase, that is, 
flow in opposite directions at the same time, they tend to aid each 
other. The currents in two or more parallel wires leading from 
the same terminal of an alternating current source would have 
about the same phase, assuming their angles of lag to be nearly 
equal, hence they tend to oppose each other. This opposition has 
the effect of increasing the drops in voltage similar to that due to 
self-induction ; in fact, the action of these wires upon one another 
is practically the same as that of one element of a wire upon the 
other elements, but in the latter case it is called self-induction. 

In practice, two alternating currents from independent gene- 
rators would not be likely to remain exactly in phase, except for a 
few seconds at a time, so that their mutual induction upon each 


132 FLECTRIC LIGHTING. 


other would produce opposing effects at one time, aiding effects at 

another, and so on as the phase changed. Supposing the frequency 

of one current to be 100 and of the other 1004 periods per second, 

the difference would be one period in two seconds, so that the 

voltage on each circuit would be raised once and lowered once 

every two seconds, causing very objectionable flickering in incan- 

descent lamps. This is avoided by increasing the difference in 

frequency between the two currents. For example, if one were 

raised 5 per cent and the other lowered 5 per cent, the difference 

would be 10 periods per second, and the fluctuations in voltage\ 
occurring at that rate would be hardly noticeable. It is better, 

however, to have a still higher rate of 15 or 20 per second in order | 
not to be perceptible or injurious to the eye. It is also possible 

to eliminate this effect by arranging or transposing the wires as 

described later. 

Means of Reducing Self-Inductance. — In equations (51) to 
(58) it is evident that self-inductance is decreased by diminish- 
ing A the interaxial distance between two wires forming a metallic 
circuit. This somewhat paradoxical fact is understood when we 
consider that self-induction is proportional to the number of mag- 
netic lines linked with a circuit, as defined on page 116. Conse- 
quently, the greater the distance between the two wires which 
constitute it, the more lines will be enclosed. Hence the wires 
should be as close together as possible in order to reduce self-in- 
ductance, the limit being the distance necessary for proper insula- 
tion, and in the case of overhead wires they must be sufficiently 
far apart not to swing too near each other. 

If two insulated wires are laid side by side, or twisted together, 
their self-inductance becomes insignificant ; and if concentric con- 
ductors are used, it disappears entirely, since the tendency to pro- 
duce magnetic lines by one is neutralized by the other, the currents 
being equal and opposite. One wire, carrying an alternating cur- 
rent and running through an iron pipe, will have large self-induc- 
tance, on account of the great number of lines which are set up 
around it; but if both wires of a metallic circuit are put in the 
pipe, the self-inductance is very small. 

Another way to reduce the drop due to self-induction is to szd- 
divide the conductor, using several smaller wires having the same 
total sectional area. 


PRINCIPLES OF ALTERNATING ‘CURRENTS 133 


Example, — An overhead line 1 mile long consists of two No. 0000 wires 
forming a metallic circuit, the distance between the wires being 24 inches. 
One mile of No. 0000 has .258 ohms resistance at 20° C., so the resistance of 
the circuit is 2 X .258=.516 ohms. The self-inductance per mile from the 
table on page 130, is 1.576 millihenrys, or .003152 henrys for the circuit. Ata 
frequency of 100 the impedance is /.5162 + (628 x .003152)? = 2.05 ohms. 
With acurrent of 40 amperes the drop due to resistance is 40 x .516 = 20.64 
volts, and the total drop is 40 x 2.05 = 82 volts. Using eight No. 6 wires in 
parallel the joint resistance would be .52 ohms, being almost exactly the same 
as before, or .52 X 8 = 4.16 ohms for each wire. Assuming the distance apart 
to be the same, or 24 inches for each pair, and neglecting the mutual induc- 
tance between the pairs, the self-inductance from the table would be 
1.912 millihenrys per mile, or .003824 for the circuit, and the impedance 
\/.4162 + (.628 X .003824)2 = 5 ohms. The current in each wire is 40+8=5 
amperes, so the resistance drop is 5 X 4.16 = 20.8 volts, and the total drop is 
5 X 5=25o0hms. In this case the resistance drop is practically the same 
as before, and the impedance drop is only 25 volts, or about 20 per cent greater 
than the simple resistance drop, while in the previous case it was 82 volts, or 
four times the resistance drop. 








The above example proves the great reduction in inductance 
drop effected by subdividing the conductor. This is sometimes 
said to be due to the use of sma/ler wires, but this is not true; in 
fact, the inductance itself is increased: by reducing the size of wire, 
as shown in the foregoing example, and in equation (53). In reality, 
the impedance drop in the second case would probably be greater 
than that calculated, on account of the mutual inductance between 
the corresponding wires of each pair; but this need not be very 
great if they are not put close together, and may be practically 
neutralized by arranging or transposing the wires, as explained 
under the next heading. 

~jAnother method of reducing the effect of inductance is to 
balance it by the effect of capacity. It was shown in connection 
with Fig. 90 and equations (46) and (49), that certain values of 
capacity in a circuit may completely or partially neutralize the 
reactance due to inductance. 

In the Stanley electric power system condensers are used upon 
the circuit in connection with the motors to balance their induc- 
tance, so that the watless current is much reduced. In other 
words, the power-factor is raised, and the drop on the line is dimin- 
ished. Theamount of capacity, A, in farads, required to neutralize 
a certain inductance, 7, in henrys, at a frequency, f, is obtained 
from (49) and has the following value: 


134 ELECTRIC LIGHTING. 


iE 


~ Lf} ee 


Synchronous alternating current motors may also be used to 
balance inductance, since they have the effect of capacity in caus- 
ing the current to lead when their field magnets are over excited. 
By regulating the field excitation the power-factor can be raised to 
practically 100 per cent. The same effect is produced by rotary 
converters, and will be considered more fully later in connection 
with the polyphase transmission and direct-current distribution 
system. | 

Means of Reducing Mutual Inductance. — The simplest plan is 
to increase the distance between the conductors, as already stated ; 
but this is limited by practical considerations, such as requirements 
for carrying the wires on the same pole. In such cases the effect 
of mutual induction would be great if the wires were arranged as 





A@ @c E G 
] oe) J K 
L M 
N Q 
e | P O 
B® @D H F 


Figs. 104, 105, and 106. Arrangement of Conductors to Neutralize Induction. 


represented in Fig. 104, in which A and & indicate the wires of 
one circuit, and C and J those of another parallel circuit. The 
wire A being very near the corresponding wire C of the other cir- 
cuit, would tend to set up an opposing £.//.F. in it, and C would 
react upon A in a similar manner. The mutual induction of B 
and JY would also have the same effect. If, however, the wires 
are placed equidistant, as shown in Fig. 105, any one conductor, £, 
will be acted upon equally by both wires, G and A, of the other 
circuit, since they are at the same distance from it. Consequently 
mutual induction between the two circuits 1s neutralized. This can 
also be accomplished by transposing the wires with respect to each 
other, at certain intervals, as shown in Fig. 106, in which the por- 
tion /V of one wire, counteracts the effect of the part Q of the 
other wire of the same circuit. Consequently the inductive action 
upon the other circuit, /AK and LJ, is nil. 


PRINCIPLES OF ALTERNATING CURRENTS. 135 


It should be noted, however, that the self-induction of either 
circuit is not materially altered by these arrangements, being de- 
pendent upon the average distance between the two wires of each 
circuit, and not upon the presence of the other circuit. 

‘¢ Skin Effect’? is the name given to the phenomenon accord- 
ing to which alternating currents tend to have a greater density 
near the surface than they have along the axis of a conductor. If 
we imagine a wire to be made up of elementary filaments parallel 
to its length, it is evident that the central or axial filament will be 
surrounded by a greater number of magnetic lines than an element 
at the surface, since each filament tends to set up lines around 
itself. This fact produces no effect upon a steady current after 
it has been established, there being no variation in the number or 
position of the lines. Hence a steady current has a perfectly uni- 
form distribution throughout the entire cross-section of a conductor 
having a uniform specific resistance. 

In the case of an alternating current, the additional lines of 
force that inclose the filaments near the axis are reversed twice 
during each period, the effect being to generate a greater back 
f:.M.F. of self-induction than for the outer filaments of the wire. 
Consequently the current density is less near the axis than it is 
near the surface. With high frequency and large conductors this 
action may be so great that there is actually a dack flow of current 
at ornear the axis. But with ordinary sizes of wire and frequen- 
cies, the effect is small. 

This “skin effect” is generally treated as an increased appar- 
ent resistance of a conductor, being called its vzrtual resistance ; 
and since it involves a larger drop in voltage and a greater loss of 
energy, it is practically the same as true resistance. 

In Fig. 107, which shows graphically the values of virtual 
resistance, RK, is the apparent or virtual resistance for a given 
alternating current, R,is the true ohmic resistance of a copper 
conductor at 20° C. (68° F.), A is the area of cross-section of the 
latter in circular mils, and fis the frequency. 

A conductor one inch in diameter has a cross-section of one 
million circular mils, so that at a frequency of 100, the product of 
A and f, is 100,000,000. Referring to Fig. 107, we find that 
oes that is, the. virtual fesistance is 21) percent 
greater than the true resistance, consequently this is too large a 


136 ELECTRIC LIGHTING. 

conductor to use at that frequency. On the other hand, No. 0 
wire has a sectional area of 105,500 circular mils, and with the 
same frequency of 100, the product A f = 10,550,000, which 
would give a virtual resistance less than one-half of one per cent 
greater than the true value, and need not be considered practically. 
Frequencies higher than 135 are rarely used in practice, and with 
a conductor one-half inch in diameter f A = 135 x 250,000 = 
33,700,000, and R, + R, = 1.03 approximately. The conclusion 
is that with conductors smaller than one-half inch diameter, the 
increased resistance due to “skin effect ” is less than 3 per cent 
for commercial frequencies. If a larger cross-section than this is 
required it should be subdivided among several wires in parallel, or 






































a) roel OF Al & F_IN MILLIONS i 


0 10 20 30 40 50 60 70 SO 90 100 
Fig. 107. Curve Showing Corrections for ‘Skin Effect.’’ 





the conductor may be made hollow or in the form of a flat bar, the 
“skin effect ’’ being greatly reduced thereby. It has already been 
shown, on page 132, that the self-inductance drop is reduced by 
subdividing conductors, but the present phenomenon is a different 
one, and should be considered separately. 

With tron conductors the virtual resistance is much greater 
than with copper or other non-magnetic metal; but iron is not often 
used to carry alternating currents, and the exact value of the per- 
meability is not easily determined,* so that formulas will not be 
given. 

Capacity of Overhead, Underground, and Submarine Conductors. 
—It is possible to predetermine the electrostatic capacity of elec- 


* Merritt, Physzcal Review, November, 1899. 


PRINCIPLES OF ALTERNATING CURRENTS. 1s We 


trical conductors, and almost all cases will come under one of the 
following heads : 


Case 1. Jusulated conductor with metallic protection ; for ex- 
ample, an iron-armored submarine cable, or a lead-covered under- 
ground conductor, having the metallic sheathing connected with 
the earth, which is the usual condition. 

Case 2. Szngle aérial conductor with earth return. 

Case 3. Metallic circuit consisting of two parallel aérial con- 
ductors. 

In the following expressions, A is the capacity in farads, * is 
the dielectric constant, Y is the internal diameter of the metallic 
covering, @ is the diameter of the conductor, % is the height above 
the ground of an aérial wire, and 4 is the interaxial distance be- 
tween two parallel wires. In cases 2 and 3, the medium being air, 
k = 1, and does not appear in the equations. This assumes that 
the conductors are bare; but if they are covered with insulation of 
ordinary thickness it would only slightly increase the capacity, & 
being greater than 1 for insulating materials. The proximity of 
other conductors may increase the capacity considerably, but their 
effect is difficult to calculate. 


Case 1. Insulated con- ; 2 Oy ee Oe 
Ue peracentimeter. = 




















ductor with metallic ae D (59) 
covering. ed, 
Tooke 10? 
K foot 7-2 
per foo shy D (60) 
Bid 
E =o 
K per mile = 38.83 & 10 
ids D (61) 
ae: 
9 sve nie 9 2 nat 
Caseuno Single aérial Popeeentineren 241.5 x 10 | 
conductor with earth me 4h (62) 
return. | a 
, br ety 
K per foot = 1,361, x 10 
4h (63) 
| ayed ae 
aay. 
9 = 
K per mile = 38.83 x 10 
4h (64) 


joy = 
og 7 


138 ELECTRICULIGATING: 


- 


Case 8. Two parallel 
aérial ‘conductors Avper centimeter 71120 Saxetoe 


forming metallic cir- of each wire ~ 08 2A (65) 
cuit. a 
Apper foot ee 30s lel 
of eachiwire 0 VR 2AM eGo) 
loge 
d 
ASpermiles | 1) 42a 
of each wire 2A (67) 
log =] 


Examples, — What is the capacity of one mile of No. 0 (A. W. G.) lead- 
covered cable, with rubber insulation .15 inch thick? Substituting in (61) for 
d, the diameter of No. 0 wire = .825 inch, and for D the external diameter of 
the insulation = .3825 + (2 X .15) = .625 inch, and for & the dielectric constant 
of pure rubber = 2.5, we have: 


38.83 & 10—9 


625 
log 355 


K per mile= = 342. x 10—-° farad = .342 microfarads. 


What is the capacity of one mile of single overhead bare No. 0 wire, 10 
feet above the ground, with earth return? Substituting in (64) the values of 
A and d, both in inches, we have: 

‘6 , x earls | 5 
AC per mile eae = 12.2 x 10— farad = .0122 microfarad. 
4 xX 120 
10g — 395 


What is the capacity of two parallel overhead bare No. 0 wires, 12 inches 
apart, and each one mile long? Substituting in (67), we have: 


2x 19.42 x 10—° 


DD < 1G 
log —355 


ie = 20.8 x 10—9 farad = .0208 microfarad. 





Means of Reducing Capacity. —It is evident from equation 
(59) that the capacity of a given length of insulated conductor with. 
metallic covering is decreased by diminishing &, the dielectric con- 
stant of the insulation, by increasing LD, the internal diameter of 
the metallic covering, or by reducing d, the diameter of the con- 
ductor. Since the capacity varies in direct proportion to &, the 
insulating material should have the minimum dielectric constant. 
Unfortunately the best insulators usually have high values for &, 
notably india rubber, gutta-percha, paraffin, and mica. ‘The dielec- 
tric constant of paper is comparatively low, and largely for that 
reason it is used for insulating the wires in a telephone cable. 
Paper is also used for the insulation of electric light and power 


PRINCIPLES OF ALTERNATING CURRENTS. 139 


cables, and would have special advantages when it is desired to 
make the capacity as low as possible. ‘This question will be con- 
sidered further under the head of insulated and underground con- 
ductors. 

_ The reduction of capacity by diminishing d@, the diameter of the 
conductor, is limited in practice by the necessity for using a cer- 
tain size in order to give sufficient current capacity, and not have 
too much resistance. It is also a fact that it is not practicable to 
materially reduce electrostatic capacity by augmenting LY, or in 
other words, by increasing the thickness of the insulation. Fig. 
108 represents a lead-covered cable, in which dis the diameter of 





Figs. 108 and 109. Reducing Capacity by Increasing Thickness of Insulation. 


the copper conductor, and JZ is the internal diameter of the lead 
covering. If the former is 4 inch, and the latter 3 inch, the thick- 
ness of insulation is } inch. In Fig. 109 the thickness of insula- 
tion is twice as great, or } inch; so that D’ becomes 3 inch, d’ 
being + inch the same as @. The capacity in the two cases will 
be in the ratio 

: 1 1 Lona Le a 
7 ~ log 2° log 8 





OO: 


bo 
jo 


That is, the capacity is reduced only 36 per cent by doubling the 
thickness of insulation. The volume of insulation in the two cases 
would be in the proportion (D? — a’) :(D" — ad") = 3: 8, which is 
an increase of 267 per cent, or almost three times as much. Since 
the amount of insulating material affects directly the cost and size 
of the cable, it would seldom pay to nearly treble this material in 
order to diminish the capacity to the extent of only 36 per cent. 
Hence in almost all cases the thickness of insulation is determined 
by its insulating qualities, and strength to withstand breakdown 
by electrical and mechanical pressures. 


140 RLECTRICOLIGHTING. 


To reduce the capacity of overhead wirés, the distance between 
them and from the ground should be increased. But even in this 
case the reduction is small compared with the increase in distance. 
Assume a horizontal wire } inch in diameter, and one mile long, to 
be strung 380 feet above the earth, and another wire of the same 
size and length to be strung 60 feet above the earth. From (64) 
the capacities in the two cases will be respectively : 


SO Coe Ome 
log 7200 

Pilfeterse yc MUS 
log 14400 


The difference between the two values is only about 8 per cent, 
although one wire is twice as high as the other. The capac.ty 
with respect to each other of two parallel overhead wires 8 feet 
apart, each being } inch in diameter and one mile long, is found 
from (67) to be 


ED sent) am 
log 860 


Increasing the distance between the wires to 6 feet, the capacity 


= 10" < 1.0" tarade—0.010 1 microtaradaana 


= 19193 < 10 = *ifaradi =" OU 9sasnicrolarad 








= 7'6 X 10—*tarade= 0076" microtarac: 





becomes 
TOM eels 
Aer = 6. 8ax «10 @'tarad =U 0G6S8emicroiancd: 
log 720 . 


In this case the capacity is reduced 104 per cent by doubling the 
distance between the wires. From these examples it is evident 
that this way to diminish capacity is hardly economical where the 
cost of construction is greatly affected by the height and distance 
apart of ‘wires, as 1s ‘the case in@pole. jinesiy) Phe smethodwor 
balancing the reactance of capacity and inductance, already set 
forth on page 133, can be applied to reducing the effect of capacity 
in electrical circuits. 


PRINCIPLES OF ALTERNATING FOLYPHASE CURRENTS. 141 


Series (banked Lets 


PRINCIPLES OF ALTERNATING POLYPHASE CURRENTS. 


THE advantages of two- and three-phase, or other polyphase sys- 
tems, apply solely to the operation of motors. In fact, such cur- 
rents are positively disadvantageous for supplying arc or incandes- 
cent lamps. Consequently this subject comes under the head of 
electric power rather than electric lighting. | However, electric 
lamps are often used upon the same circuits with polyphase motors, 
and in many cases energy is transmitted over long distances by 
polyphase currents, to be converted into direct currents for local 
distribution to lamps; so it is necessary in the present volume to 
consider the principles of polyphase systems, and the methods of 
operating lamps upon them. 

A two-phase current may be regarded as, and in most cases 
actually consists of, two dzstzmct single-phase currents, flowing in 





{ 

1 

' 

! 

1 

E B H 
Fig. 110. Two-Phase Current. 


separate circuits. There is often no electrical connection between 
them, their only relation being that of ¢zme. That is, they differ 
in phase. This condition is shown in Fig. 110, in which the curve 
ABCD represents one alternating current, and E/GAH// represents 


142 BLBCTRICOTILAIING 


- 


another, the difference in phase being 90°, the maximum value 
G of the second occurring 90° behind the maximum point A of the 
first, and so on for other corresponding points. If there is no lag 
of either current, the same curves can be taken to represent the two 
E.M.Fs, and with the same lag for both currents they would still 
be 90° apart in phase. If the lags were not equal, then the phase 
relation would be altered correspondingly. The two /.4/.F:s or 


B 





E 
Fig. 111. Two-Phase, Four-Wire Circuit. 


currents might have different maximum values, or different wave 
forms, but in practice they are usually made as nearly alike as pos- 
sible. It is evident also that the difference in phase might be made 
anything between 0° and 360°; but it is almost always designed to 
be 90°, or one-quarter of a period, and for that reason is often 
called a guarter-phase current. ‘“[wo-phase currents may be gene- 
rated by two separate alternators, but in order to preserve the phase 
relation it would be necessary to have their shafts coupled or posi- 


B 





E 
Fig, 172. Two-Phase, Three-Wire Circuit. 


tively connected together. In practice, a two-phase current is usu- 
ally generated by two separate windings upon one armature, the 
machine having the same general form as a single-phase alternator. 

The two circuits may be kept entirely separate, as in Fig. 111, 
lamps Z being connected to each, in which case four wires are 
required. In order to save one wire it is possible to use a common 


PRINCIPLES OF ALTERNATING POLYPHASE CURRENTS. 143 


return conductor for both circuits, as in Fig. 112, the dotted por- 
tion of one wire, J, being eliminated by connecting across to C at 
Mand N. For long lines this is economical, but the interconnec- 
tion of the circuits increases the chance of trouble from grounds 
or short circuits. It is alsoa fact that the current in the conductor 
C will be the resultant of the two currents, dif- 
fering by. JO" siniephase, ~ brom:-thee principle’~ P 
shown in Fig. 93, the value of this resultant 
ievtoundsin Piewils to be Ok = V2 OP = 
1.41 x OP the two-phase currents being repre- 
sented by the components OP and OQ at right Oo 
angles to each other. Consequently the result- 1%. 773 Resullant of 
ant current in C is 1.41 times that flowing in 

either B or & in Fig. 112 and the cross-section of the wire C 





should be 41 per cent greater. 

A three-phase current consists of three alternating currents, 
differing in phase, as indicated in Fig. 114. One current is repre- 
sented by the curve /AZ, another by the curve J/WVO, and the 
third by the curve PQR, the maxima points /, W/, and Q (or other 
corresponding points) being 120° apart in the ideal case, and ap- 


§ M Q O 





Fig. 114, Three-Phase Currents. 


proximately so in practice. These three currents might be carried 
in three entirely separate circuits requiring six wires, being analo- 
gous to the two-phase, four-wire system in Fig. 111; or one com- 
mon return conductor may be used, thereby saving two wires, and 
reducing the total number to four, as shown in Fig. 115. The 
armature windings and their phase relation are represented dia- 


144 ELECTRIC LIGHTING 


grammatically by the coils J7A, A7B, and MC, the three main con- 
ductors by AZ, BG, and C/, the common conductor being indicated 
by the dotted lme 47. The lamps Z, Z, Z, are connected across 
between the common point /V and the three main conductors. 

If the three circuits are balanced (i. e., have equal currents) the 
common conductor M/W will carry no current, and may be dis- 
pensed with. This is a most interesting and important feature of 





Fig. 115. Three-Phase Circuits with Y Gonuecuen. 


the three-phase system. The simplest way to understand it is to 
consider that each wire acts as the return conductor for the other 
two. In other words, the algebraic sum of the three currents 
meeting at the common point /V is equal to zero; consequently 
Kirchhoff’s law is fulfilled. This fact is shown in Fig. 114, the 
algebraic sum of the ordinates of the 
three curves being equal to zero at any 
point. For example, at SR the ordinate 
of curve J7/VO is zero, and the ordinates 
of the other two are equal in value, but 
opposite in sign. At 7A the sum of 
the two positive ordinates of the curves 
MN and PQ are equal to the negative 
ordinate of the other curve /KZ, be- 
cause. 1 7) = "sins 0° == teand kh sem 
90° =\1, and so on for other points. 
Fig. 116. Kesultant Current, re pees 

Tirbe PAu The same principle is proved in Fig. 

116, in which a balanced three-phase 

current is represented by three equal vectors at 120° with respect 
to each other. Two of these currents, OZ and OU, are equivalent 
to their resultant OR, which is equal and opposite to the third cur- 
rent OS; consequently the resultant of all three currents is zero. 
In the operation of motors the three currents are usually equal, 
all three wires being connected to each machine, so that the fourth 





PRINCIPLES OF ALTERNATING POLVPHASE CURRENTS. 145 


wire WN, in Fig. 115, is superfluous ; but for electric lighting this 
extra conductor is required, unless the lamps on the three circuits 
are balanced. If the currents in the three branches are not equal, 





Fig. 117. Three-Phase Circu.ts with A Connection. 


then the wire J/W carries the difference between them, so that its 
function corresponds closely with that of the neutral conductor in 
the ordinary three-wire system described on page 70. 

Another method of connecting three-phase circuits is shown in 
Fig. 117, and is called the A (delta) connection, the arrangement in 
Fig. 115 being designated as the Y connection. In either of these 
cases any lamp Z is fed simply by 
the £.M/.F. due to a single arma- 
ture winding, J7A in Fig. 115, or 
OP einmebion slits elf ehowever, v2 
lamp is connected across the outer 
terminals of the Y circuits, it re- 
ceives a voltage which is the resul- 
fate Ore two 17778" that’ are in 
series, but differ by 120° in phase. 
minseissshown mo bio. sl18, 0A, 
DB, and DC representing respec- 
tively the £.17.F.s of a three-phase 
armature winding with Y connection. Assuming the £.J/.F. of 
each phase DC to be 100 volts, then the £.17./. between A and 
C will be V3 = 1.78 times as great, or 173 volts. 

Production of Rotary Field by Two-Phase Current. — An iron 
ring, wound with insulated wire, as represented in Fig. 119, is sup- 





Fig. 118. Relative Voltage of A and Y 
; Connections. 


plied with two-phase currents at the four equidistant points A, BA, 
C, and D, the two conductors of one phase being connected at A 
and #, and those of the other phase at Cand D. Considering only 
one current, and assuming it to enter at A, the direction of wind- 
ing. is such that it will produce a south pole at A, and a north pole 


146 ELECTRIC LICHTING. 


at B, so that a compass needle placed inside the ring would tend 

to point vertically upward as indicated by the dotted arrow. ‘This 
| condition is represented at 1, in 
Figs 20, the tcurment eee 
having its maximum positive 
value, and the other current, 
PEO, being ezeromeaten Davee 
stant. A moment later, the first 
current has decreased somewhat, 
and the other has increased, so 
that they are equal eine iis 
case, each will tend to produce. 
a south pole where it enters the 
ring, at A and VL respectively, 
so that a resultant polarity is 
produced midway between, as 
shown at 2 by the arrow inclined at 45°. The next instant, at 
90°, the: current 2 27 has fallen to?zerofand. the currents 14s 
reached its maximum, so that the arrow takes a horizontal position, 
as represented at 8. Again at 135°, the current Z J/ has reversed, 
tending to make a south pole at the bottom of the ring, and the 
needle will incline downward at an angle of 45°, as shown at 4. 





Fig. 119. Ring Supplied with 
Two-Phase Current. 






oO 


1 2 3 4 5 6 7 8 9 


Fig. 120. Magnetic Resultants due to Two-Phase Current. 


By following the successive conditions, the needle will be found to 
take the various positions represented at 5, 6, 7, 8, and finally at 
9, it returns to its original vertical direction, the current having 
completed one period. Thus the needle tends to be carried around 
continuously by the shifting resultant field, so long as the ring is 
supplied with two-phase currents. 


PRINCIPLES OF ALTERNATING POLVPHASE CURRENTS. 147 


Principle of Polyphase Motors. — It is this capability of produ- 
cing continuous rotation that gives the polyphase currents their 
interest and value, since it enables motors to be operated very suc- 
cessfully. The ring with the magnetic needle, in Fig. 119, illus- 
trates the principle of the syzchronous polyphase motor, since the 
armature revolves in exact synchronism with the phases of the 
currents. If the needle is replaced by a cylinder of laminated iron 
wound with conductors, like an ordinary armature, except that they 
are short-circuited, it is found that it will revolve also; but in this 
case the speed is a little less than that of a synchronous armature, 
the difference being called the s/f, usually amounting to from 1 to 
© per cent. This slip represents a relative motion of the rotating 
field, with respect to the armature conductors; consequently the 
latter are cut by the lines of force, thereby inducing currents in 
them. It is the action of the field upon these induced currents 
which causes the armature to revolve, this type being called the 
induction motor. It is aremarkable fact that no current is sup- 
plied to the moving part, so that it need have no electrical connec- 
tions made to it except for purposes of starting and regulation. 

In some cases the construction is 
modified so that the part in which the 
currents are induced revolves, and the 
other part is stationary. For this 
reason, and because no energy is 
supplied directly to the so-called arma- 
ture, it is considered more correct to 
distinguish the two elements of an 
induction motor as vofor and sfavor, 
or primary and secondary. 

The Action of Three-Phase Currents Fig. 121. Ring Supplied with 
in producing a rotary field is quite three Rips es Curent 
similar to that described for two- 





phase currents. The ring in Fig. 121 is wound as before, but 
ToeecuLrentmismicdiiledt three equidistant points, /7, Y,.and 2, 
instead of at four points. Taking the instant when the current 
flowing in at H is a maximum, two currents flow out at Y and Z, 
each having one-half the value of the current entering at 7 This 
tends to produce a south pole at /, and two north poles at Y and 
Z respectively. The resultant due to the latter is a south pole at 


148 ELECTRICALIGHITING. 


7, midway between Y and Z, consequently a magnetic needle 
would take the position shown by the dotted arrow. (This condi- 
tion is represented at 0° in Fig. 114.) A moment later (at 60° in 
Fig. 114) currents enter at both / and 7, and a maximum current 
flows out at Y, hence the needle would point toward VY. At the 
end of another one-sixth of a period (at 120° in Fig. 114), the 
maximum current will enter at Z, and the needle would turn to 
that point, and so on until it had made a complete revolution in one 
period of the alternating current. 

Actual Forms of Polyphase Motors. — The synchronous type of 
polyphase motor is similar in principle and construction to the cor- 
responding generator, in fact, two identical machines may be used, 
one as generator and the other as motor, the same being true of 
single-phase alternating, as well as direct-current machines. In all 
these cases the field magnets must be supplied with direct current 
either from a separate exciter or from the machine itself, which, 
if it is an alternator, must be provided with a commutating device 
for that purpose. 

The advantage of the polyphase over the single-phase synchro- 
nous motor is. the fact that the former is self-starting, owing to the 
fact that it exerts some rotary effort even when standing still. In 
this case it acts as an induction motor, the armature being supplied 
with polyphase current, but the field circuit is left open until syn- 
chronous speed is reached. On the other hand, the single-phase 
motor has no starting torque, and has to be provided with some 
special device in order to bring it up to synchronism. 

The practical forms of induction motor are self-starting with 
considerable torque, but they are generally arranged with some 
means for introducing resistance into the secondary circuit, in 
order to give them full torque when starting, and to prevent a 
great rush of current at-that time. 


ay ALR af 
LL ph AY’ anf Cf g 
A ; ee. ; <r 
a7 et A) 


TRANSFORMERS. 149 


eral Pea boxy 
TRANSFORMERS. 


A TRANSFORMER consists essentially of two separate coils of 
insulated wire wound or placed upon an iron core. One of these 
coils, called the primary, receives alternating current from some 
source ; and the other coil, called the secondary, delivers alternating 
current to any circuit that may be connected to its terminals. The 
action depends upon the physical principle that an alternating cur- 
rent sets up an alternating magnetic flux which tends to induce an 
alternating £.47.F. in a conductor that encloses the flux. The 
function of a transformer is to convert electrical energy at one 
voltage into electrical energy at another voltage. 

For example, a transformer is supplied with an alternating cur- 
rent of 1000 volts and 10 amperes, and it delivers a current of 100 
volts and about 97 amperes. The input is 10 k. w., and the output 
is about 9.7 k.w., since there are losses amounting to about 3 per 
cent; that is, the efficiency is 97 per cent. In most cases trans- 
formers are used to reduce a high-voltage supply of energy into 
low-voltage energy that is safe and convenient for operating lamps, 

motors, and other devices. Sometimes they are employed to raise 
the pressure in order to transmit energy economically over long 





Fig. 122, Simple Transformer Circuit. 


lines. The former are called step-down and the latter step-up 
transformers. For the sake of simplicity, a transformer is often 
represented as consisting of a ring of iron, CH, in Fig. 122, with 
a primary coil, ?, and a secondary coil, S, wound upon it. In the 


159 ELE CLRICIEIGHTINVG 


step-down type, which is far more common, the primary, /, is 
composed of many turns of fine wire, being connected to the high- 
voltage supply conductors Y and £, leading from the alternator, 
A, and the secondary, S, consists of comparatively few turns of 
large wire, to which the local or secondary circuit, /G, and lamps, 
L, are connected. The ratio of voltages of the two coils is sub- 
stantially the same as the ratio of the number of turns of wire that 
they contain. 

Construction of Transformers. — In practice the arrangement 
represented in Fig. 122 would not be satisfactory for supplying 
constant potential to lamps, etc., because the flux produced by the 
primary P would not all pass through the secondary S, the mag- 
netic leakage across from C to Af being considerable, especially 
when the current in the secondary circuit is large. 

To avoid this magnetic leakage, the 
primary and secondary coils are placed 
close together, in many cases being 
wound one upon the other, as in Fig. 
123, which shows the core and coils of 
a small General Electric type F trans- 
former. In other forms the coils are 
subdivided and placed side by side alter- 
nately, as in Fig. 124, which illustrates 
a Westinghouse 25 k.w. transformer 
with the casing removed. 





In these and other types of constant 


Fig. 123. Transformer with : ; 
Superposed Coils. potential transformers the object is to 


reduce the magnetic leakage to a mini- 
mum, by so arranging the coils and magnetic circuit that practically 
all the flux produced by the primary must pass through the second- 
ary. This condition is in conflict with the necessity for very high 
insulation between the primary and secondary coils to prevent the 
dangerous high-voltage current from breaking through to the low- 
voltage circuit. To avoid magnetic leakage, the coils are closely 
sandwiched together; but to give the best insulation they should 
be separated. The insulation is obtained, however, by completely 
covering each coil with several spiral windings of tape and mica- 
cloth, as represented in Figs. 123 and 125. Sheets of fibre, mica- 
cloth, etc., are also placed between the coils, in addition to which 


TRANSFORMERS. tol 


special means are generally provided to avoid trouble through fail- 
ure of insulation. These will be discussed under the head of 
Transformer Protective Devices. } 

The coils themselves consist of ordinary cotton-covered round 
or flat copper wire. ‘These are wound and insulated separately ; 
the proper number and 
arrangement of primary 
and secondary coils are 
then assembled, being held 
in position by a suitable 
framesOlSUppOnie = Lhe 
strips of thin sheet iron (8 
to, Loomis = 005eto 015 
inch thick) which form the 
core are next placed around 
the coils as illustrated in 
Fig. 125. One method of 
building up the core is 
shown in Fig. 126, being 
the plan followed by the 
General Electric Company 
in the larger type // trans- 
formers. Two different 
sizes of strips, A and #, are 
used, one being longer than 
they others se) Aw layer rot 
these is laid (Fig. 126); 
then the next layeris placed 
so that it breaks joints with 
the first, as indicated by 
the dotted lines ; and so on 
until the core is completed, 
the coils shown in section 





Fig. 124. Transformer with Casing Removed. 


at CC being entirely surrounded by iron, which forms two closed 
magnetic circuits. The small round holes in the iron strips are 
slipped over vertical bolts, which serve to locate and hold them 
im place? “A\.core of the form’ illustrated in Fig’* 123 is gen- 
erally made of sheet iron. punched out in the shape shown in 
Fig. 127. Each layer consists of a single piece; but it is cut 


Way: ELECTRIC LIGHTING. 

through at Z and J/, forming a tongue, 7, which is sufficiently 
flexible to be put through the coils (Fig. 123). The next piece is 
placed in the opposite direction, as indicated by dotted lines, in 
order to distribute the joints in the magnetic circuit. 


Method of Building Large Transformer. 


Fig. 125. 





For actual use a transformer is enclosed in a cast or wrought 
iron case to protect it from mechanical injury and dampness. In 
many instances this case is filled with oil to facilitate the dissipa- 
tion of heat and to improve the insulation. The Stanley trans- 


TRANSFORMERS. sg 


former (sizes 2 to'10 k.w.) for out-door use, having hanger irons 
with hooks to fit over cross-arms on poles, is shown in Fig. 128. 
Copper Loss in Transformers. This quantity is simply the 
heating “Or 7/7 A loss 
which always occurs 
whenever any current, . 
I, flows through a resis- 
tance As sli /iicathe 
primary, -and- 72y the 
secondary ; current, 7’ 
and 2A) | betas) thes re- 
spective resistances of 





the primary and secon- 


dary coils, then the total Fig. 126. Transformer Coil. 
copper loss, W., in watts is: 
W, = hy dee ae A ae (69) 


Calling W, the primary input in watts, we have 

J"? Ie ae fil? RR 
From (69) it is seen that this loss varies as the square of the 

load in amperes. Its exact value depends upon the design of the 


transformer and working conditions ; but in most commercial types 
at full load it is about 3 per cent for 1 k. w., and about 1 per cent 





Percentage of copper loss = (69a) 


for 100k. w. capacity. Ina very 
large General Electric transformer 
having 1875 k. w. output, used at 
Niagara, the copper loss is a little 
lessethane? perecent.= 4 Ittis also 
evident from (69) that the copper 
loss increases with the resistance; 
and since the latter is greater 
with higher temperature, the loss is larger when the transformer 
becomes heated by the current or in any other way. The maxi- 
mum allowable rise in temperature is 50° C. above that of the 
surrounding air (Amer. Inst. Elec. Eng. Standard); and since 
the resistance is increased about .4 per cent for each degree, the 
resistance and copper loss are about 50 x .004 = 20 per cent 





Fig. 127. Transformer Coil. 


* Electrical World and Engineer, Nov. 18, 1899. 


154 , ELECERICOLIGHTING. 


higher at maximum temperature. This point will be considered 
more fully later under Regulation. 

The copper loss injuriously affects the action of transformers in 
three ways: 

1. Copper loss reduces the efficzency. 

2. Copper loss produces Aeat that may injure the insulation. 

5. Copper loss interferes with the vegudatzon of constant po- 

tential transformers. 

Hachwolsthese 
effects will be consid- 
ered specially under 
the respective head- 


ings, — efficiency, 
heating, and regula- 
tion. 


| Iron or Core Losses 
r ‘in’ Transformers; 2. 
These are due to hys- 
teresis and eddy cur- 
rents in the core, and 
are quite similar to 
the core losses in a 
generator or motor. 
They differ from the 
copper losses in the 
fact that they are 
nearly constant for all 
loads, whereas we 
have just seen that the latter vary as the square of load. These 
statements apply to constant potential transformers, these being 
by far the most common. The case is exactly the reverse for the 
constant current type, in which the copper loss in the secondary 1s 
constant, and the iron loss varies with the load. In most practical 
types of transformer the iron losses are about equal to the copper 
losses at full load. This is not a necessary condition, it being an 
easy matter to design a transformer in which the iron losses are 
much greater than the copper losses, or véce versa. In fact, they 
are mutually related, so that increasing one tends to decrease the 
other. 





Fig. 128. Transformer for Out-door Use. 


TRANSFORMERS. LoD 


For general use it has been found best to make the two losses 
approximately equal; but for special cases, where constancy of 
voltage is important, or where transformers operate with consider- 
able load most of the time, the copper loss may be reduced at the 
sacrifice of increased iron loss. If, however, constant voltage is 
not important, and a transformer is likely to run at light loads a 
great part of the time, then the iron loss should be diminished at 
the expense of the copper loss. Ordinarily these differences require 
transformers to be specially designed for the purpose; but varia- 
tions in frequency, voltage, or other conditions will alter the 
relation between the two losses. 

The hysterests loss in watts, W,, 1s: 


Wi =4 V7 BY (79) 


In this expression, V is the volume of the iron core in cubic 
centimeters, f is the frequency in cycles per second, B is the maxi- 
mum flux density in lines per square centimeter, and y is a constant 
depending upon the quality of the iron. For high-grade annealed 
sheet iron suitable for transformer and armature cores, the value of 
7 is usually between 2 x 10° and 3x10. In calculations where 
the exact value is not known, an average value of 2.5 x 10-° may 
be assumed. The ordinary values of B, the maximum flux density, 
for various sizes of transformer and frequencies are given on page 
157. 

Ageing of Transformer Iron. About 1894 attention was called 
to the fact that the iron cores of transformers became changed 
after being used for some time, the hysteresis loss increasing con- 
siderably. Investigations showed that the core loss of some com- 
mercial types of transformers rose to two or more times the initial 
value after a few months’ operation. It was found thai this was 
due to heat, the same effect being produced by heating the iron 
in any other way. This phenomenon depends upon the mechani- 
cal and chemical character of the iron, but the exact effect of the 
different impurities has been found to be difficult to determine. By 
experience and the exercise of great care, manufacturers have been 
able to avoid this increase of hysteresis loss, so that transformers 
made at present have very little more core loss after long periods 
of use. Professor W. E. Goldsborough has given * the results of 


* Paper before National Electrical Light Association, May, 1899. 


156 ELFCTRI COACHING. 


tests made on several of the most prominent types of transformer, 
and these show that the core loss remained practically constant for 
800 hours at full load. These tests were made in a room where 
the temperature was about 25° C., and the full load was applied 
for ten and a half hours a day. This is fully as severe as ordinary 
practical service ; nevertheless, the temperature of the cores did not 
exceed 75° C., allowing the standard rise of 50° C. Up to this 
point it is found that the ageing effect does not occur; but above 
80° it begins, and at 100° it becomes considerable, increasing with 
the temperature up to about 200°, beyond which it falls again. 

The conclusion is, that transformer cores should not be run, 
even for a short time, at temperatures.exceeding 80° C. At full 
load the allowable rise is 50° C.; hence the room temperature must 
not be greater than 30° C., or 86° F. On the other hand, in very 
hot weather, or in an engine-room where the temperature may be 
10 or 20 degrees higher than this, transformers should not be run 
at full-load, or may be operated for shorter periods of time, so that 
they do not attain maximum temperature. This matter is suff- 
ciently important to demand attention, and every one installing or 
using transformers should guard against the possibility of the core 
temperature rising above the point at which ageing begins. ‘This. 
limit may be ascertained from the makers. 

Lhe eddy or Foucault current loss in the core in watts, W,, is 


W.=b VPP B (71) 


In this expression ¢ is the thickness of the laminations in centi- — 
meters; V, f, and B have the same significance as in (70), and & 
is a constant depending upon the specific resistance of the iron. 
In the iron ordinarily used the value of 4 is about 1.6 x 10°". 

In a paper read before the American Institute of Electrical 
Engineers, May, 1900, Mr. Fitzhugh Townsend claims that the 
eddy current loss is proportional to B** instead of B’. 

This equation assumes that the sheets of iron forming the core 
are properly insulated from each other, otherwise the loss is greater, 
because the eddy currents flow from one sheet to another as if the 
core were a solid mass of iron. 

Since the eddy current loss in (71) varies as ¢?, the square of 
the thickness of the iron plates, it may be reduced to a very small 
value by making them very thin. On the other hand, the insula- 


TRANSFORMERS. 157 


tion and unavoidable space between the plates is about 2 mils, so 
that in practice a thickness of 10 to 15 mils is generally adopted 
in order that the proportion of iron in the total volume of the core 
shall be high. Assuming an ordinary thickness of 12 mils for 
the plates and a distance between them of 2 mils, the actual iron 
in the core is ae = .86 of the total volume. With these rela- 
tions the eddy current loss constitutes about 20 per cent of the 
core loss, the hysteresis loss making up the remaining 80 per cent. 
In some cases the thickness of plates is reduced to 7 or 8 mils, so 
that the eddy current loss is only 8 or 10 per cent of the core loss ; 
but this tends to increase the volume of the core as well as the 
weight of copper, and involves more labor in construction, hence 
the final gain is doubtful. 

The permissible rise in temperature being 50° C., the resistance 
of the iron core increases about 20 per cent after a long run at full 
-load, hence the eddy current loss is reduced in the proportion 120: 
100, or in other words it is about 17 per cent less. But the eddy 
current loss is only about 20 per cent of the iron loss, so that the 
latter is reduced 3 or 4 per, cent at full working temperature, 
hysteresis being constant. 

Flux Densities in Transformer Cores. The hysteresis loss 
varies as B'* in (70) and the eddy current loss as B’ in (71) or 
B**, in which B is the flux density, consequently the latter is kept 
at a low value in transformers in order that the core loss shall be 
small. Different designers adopt various densities, average figures 
being given in the following table. 


ORDINARY FLUX DENSITIES IN TRANSFORMER CORES. 


MAXIMUM LINES PER SQUARE CENTIMETER. 


Frequency. 1to5k.w. 10 to 25k. w. | 100 to 500 k. w. 





7500 6500 5500 


6500 5500 4500 
5000 4500 4000 
4000 3500 3000 
3500 3000 2500 











The density is decreased with higher frequency in order to 
keep the iron losses in (70) and (71) nearly the same for a given 
volume of core. These densities are much lower than those 


158 ELECTRICALIGHTING. 


allowed in the armature cores of generators and motors which are 
often as high as 15,000 or 16,000 lines per square centimeter. The 
reason for this is the higher efficiency of 97 or 98 per cent which 
is expected of transformers compared with 92 to 94 per cent for 
machines. ‘The former often operate for long periods at very light 
load, while generators usually have one-half to full load while they 
are running, consequently the constant core loss is a more serious 
matter in transformers. 

Exciting Current. When the secondary circuit of a transformer 
is open and the primary circuit is closed, a certain current flows in 
the latter. This is called the exciting current, being also known 
as the /eakage current, open-circuit current, and magnetizing current. 
It consists of two components, one of which supplies the energy to 
make up the transformer losses, and the other produces the mag- 
netization of the core. The former represents true power in watts 
being practically equal to the iron losses, and the latter is apparent 
power being wattless. The total value of the exciting current de- 
pends upon the design and size of the transformer, but is ordina- 
rily about 5 per cent for 1 k.w., and about 2 to 1 per cent in 
sizes of 25 to 100 k. w. or larger. 

The power factor of the exctting current at no load differs con- 
siderably in the various types, but is usually about 70 per cent. 
Since this is equal to the cosine of the angle of lag, it follows that 
the no-load primary current lags about 46° with respect to the 
primary impressed 4.47.7’. It is evident also that the energy com- 
ponent of the current is about equal to the magnetizing compo- 
nent. When a transformer is loaded even slightly, for example, to 
one-tenth of its normal capacity, the power factor rises to very 
nearly 100 per cent, and the primary current is practically in phase 
with the primary impressed £.1/./., provided the load is non-induc- 
tive, which is usually the case in electric lighting. If, however, 
induction motors or other forms of inductive load are present, the 
power factor will be less than 100 per cent, and the current will 
lag behind the £.J7.F. as in any alternating-current circuit. 

The above statements apply to transformers having closed 
magnetic circuits. In the so-called “hedgehog’”’ type with open 
magnetic circuit consisting of a simple straight core, the no-load 
exciting current is about ten times as great, being more than one- 
half of the full load value in a 3 k. w. size, with a power factor of 


TRANSFORMERS. 159 


only .063, which is also about one-tenth as much as for closed mag- 
netic circuit.* On account of its low-power factor this large excit- 
ing current does not involve directly any greater loss of power in 
true watts. But it uses up the current capacity of the generators, 
lines, etc.; the heating effect and drop for a wattless current being 
the same as for any other current having the same value in 
amperes. Furthermore, it reacts injuriously upon the regulation 
of generators and transformers, greatly increasing their drop in 
volts. For these reasons the closed magnetic circuit has been 
adopted almost universally. In fact, the greatest care is exercised 
in making the magnetic circuit as complete as possible, the effect 
of joints being reduced to a minimum, which also reduces magnetic 
leakage, as explained on page 150. 

To prevent the flow of this exciting current, magnetic cut-outs 
have been devised to open the primary circuit automatically when 
the secondary circuit is open. It is objectionable, however, to 
open and close the primary, (high voltage) circuit whenever the 
load is thrown off or on, so that this arrangement is seldom used 
in practice. Another plan is to open the primary lines at the 
station during the hours that the current is not required. This is 
customary in smaller systems, and is possible on certain circuits of 
large systems, but it cannot be applied generally in important 
plants. 

Efficiency of Transformers. ‘The efficiency of a transformer is 
the ratio of the watts output W, measured at the secondary ter- 
minals to the watts input measured at the primary terminals W,. 
Since the losses occurring in a transformer are: W, the copper loss 
from (69), W,, the hysteresis loss from (70), and W, the eddy cur- 
rent loss from (71), it follows that the output is sede to the input 
minus these losses, hence 
W._ W,- (W.+ W+ W) 
ne SRR: 

The efficiency is very high for transformers made by the best 
manufacturers, being about 98 per cent at full load for sizes of 25 
k. w. or larger, and 94 or 95 per cent at one-quarter-load. ‘This 
is higher than the efficiency of almost any other practical appara- 
tus, nevertheless it is found that the aggregate losses are large, and 
form a heavy item in the cost of alternating-current supply, because 


(72) 





Eiiciency, = 


* The Alternate Current Transformer by J. A. Fleming, London, 1896, p. 567. 


160 ELECTRIC LIGHTING. 

transformers run fora large part of the time with small loads, 
especially in electric lightning. 

~ Calculation of Transformer Efficiencies. Knowing the iron and 
copper losses at any given load, it is a simple matter to calculate 
these losses and consequently the efficiency at other loads. For 
example, a 10 k. w. constant-potential transformer at full rated 
load and temperature has a copper loss of .16 k.w. or 1.6 per 
cent, the iron loss being the same. Since transformers and most 
other apparatus are rated by their output, the efficiency would be 


output _ 10 
input 10+ .16-+.16 





==1 0.0. per cent, 


At three-quarters load the output is 7.5 k.w., the iron loss is 
the same as before, being practically constant ; the copper is pro- 


OPM 
ab SC A, LO =n Ww. 
4% q%* D O9ekeawx7so 


portional to the square of the load, or 


(es: 
Toc. 16-2. 09 
culating in a similar manner the efficiencies at other loads, we 


= 96.8 per cent. Cal- 





that the efficiency would be 


obtain the following results : 























12.5 
Efficiency at 25% overload = SIR One 96.8% 
10 
rated load = 104.16 +16 ~ 96.9% 
7.9 
4 ‘ three-quarters load = 754 164 09 7 = 96.8% 
j 5 d 
one-half load = cn Goad a = 96.2% 
2.5 
# “ one-quarter load = 554 162.017 = 93.5% 
1 
“ one-tenth load = Wis 1 ee 86.1% 
Oo 
« —_ one-twentieth load = ; aq = 10.1% 


Pt eke 0004 


In order to bring out the comparative effects of the two losses, 
let us calculate the efficiencies of two other transformers, one hav- 
ing a copper loss of .08 k.w. and an iron loss of .24 k. w., the 
other having .24 k.w. copper loss, and .08 k.w. iron loss. In 


TRANSFORMERS. 161 


all three cases the sum of the losses is assumed to be the same at 
full load (10 k. w.), being .82 k.w. The results are given in the 
following table: 


EFFICIENCIES OF TRANSFORMERS WITH DIFFERENT RATIOS OF LOSSES. 


Losses 1n K. W. ’ Ourput in K. W. 





Copper Iron. 





JAB Ames 
08 24 
24 08 





























The above efficiencies as well as the losses at different loads 
aresplotted: as cunves: in bie. 129, 6A study<of the table and 
curves brings out many important points regarding transformers : 

1. The sums of the losses being equal (.82 k. w.) at rated load 
(10 k. w.) the efficiencies are the same for that particular output. 

2. Transformer No. 1, with copper and iron losses equal at 
rated output, has an efficiency which is a maximum at that point, 
and is nearly constant (96.2 to 96.9%) from one-half load to 25 
per cent overload, being well suited to this range. 

3. Transformer No. 2, with large iron loss which is constant, 
has maximum efficiency with considerable overload (about 50%), 
but is low in efficiency below three-quarters load. Its small copper 
loss, however, makes its regulation excellent, the resistance drop 
being only .8 per cent at rated load. 

4. Transformer No. 3, with small iron loss, has opposite charac- 
teristics, its efficiency being highest at one-half load, and 92.4 per 
cent at one-tenth load, which is remarkably high. At overload the 
efficiency falls rather rapidly. The regulation is not good, since the 
resistance drop alone is 2.4 per cent at rated output. It would be 
adapted for power or other use where the load was light most of the 
time, and where such a variation in voltage is not objectionable. 

5. From the point of view of efficiency only, the copper loss 
in constant potential transformers is less objectionable than iron 
loss for variable load, since the former varies as the square of the 
current, and thus adjusts itself to the working conditions. This 
is shown by comparing Nos. 2 and 3; the latter with relatively 
large copper loss has an efficiency of 92.4 per cent at one-tenth 


162 ELECTRICUIIGHTING. 


- 


load, while the efficiency of the former, with very small copper 
loss, is only 80.6 per cent. 


100 
































































































































































































neeeS 
+ ee) P| ee 
BeCCe 
Be BBR 
coo CEE 
EES: | 
ce EZ 
Ek Elen 
e Pieri 
/| 
Bui JL 
Pe ApS: 
nay o5 
O [| : 
oats Geaaa & 
wT ag} & 
3 (EGMIMISP 9 
q LJ 
: aaee 2 
Oo 
a AIRE 
TE 15 
~ | 
z 
|_| 
10 
san 
.05 
OED 5. eo 10 Oss 
OUTPUT IN K, W. 
Fig. 129. 


6. On the other hand, the effect upon regulation is exactly the 
reverse, as set forth on page 164. 

The calculations of efficiency as made above might be criticised 
on the ground that the increase in resistance due to temperature 
rise at full load, is not taken into account. 


TRANSFORMERS. 163 


The resistances of primary and secondary coils were taken in 
all cases as constants, the value being that for continuous running 
at rated load commonly called the resistance “hot.” This makes 
the calculated efficiency correct at that load, and the error would 
be slight for other loads. For example, the efficiency of No. 1 at 
half-load is given as 96.2 per cent, and with allowance for reduced 
temperature it would become 96.25 per cent. The difference is so 
insignificant that it does not warrant the trouble in making the 
correction. 

The reason why the discrepancy is not larger is to be found in 
the fact that the copper loss at light loads is much reduced, and a 
small variation in it has very little effect. | 

Furthermore, the heating is only partly (about one-half) due to 
the copper loss, so that the temperature does not change in pro- 
portion to it. The conclusion is that the resistances “hot” (at 
full load) may be taken to calculate efficiencies at any continuous 
load from zero to 25 per cent overload with very trifling error. 

All-day Efficiency. Since the efficiency of transformers varies 
considerably with the load, as shown in Fig. 129, it is evident that 
the changing output which occurs in practical working will give an 
average or all-day efficiency which is usually less than the maxi- 
mum. For purposes of comparison, the transformer is assumed to 
run fully loaded for 5 hours, and with no load for the remaining 19 
hours. On this basis the all-day efficiency is commonly reckoned; 
but in any case where the actual periods and amounts of output 
are known, the determination can be made accordingly. Applying 
the conventional 5 hours full load and 19 hours no load to the three 
transformers whose efficiency curves are shown in Fig. 129, we 
find the following : 


ALL-DAY EFFICIENCY OF TRANSFORMERS. 


Iron Loss CopreR Loss | Totat Lossezs | Totrat Outreut ALL-Day 
In K.W. In K. W. In K.W. EFFICIENCY. | 


Hours. Hours. Hours. Per Cent. 








5 x10 
='50 


50 
50 








164 FL PCTRICH LIGHTING. 


This table demonstrates that transformer No. 3 with small iron 


loss which is constant has a very high all-day efficiency of 94.1 per 
cent, while No. 2 with large iron loss has only 89 per cent. The 
losses per day of No. 2 are 6.16 k.w., being nearly twice those of 
No. 8, which are 3.12 k.w. Inthe course of a year, the total out- 
put of each transformer would be 365 x 50 = 18250 k.w. hours, 
and the losses of No. 2 would amount to 365 X 6.16 = 2248.4 
k.w. hours, or one-eighth as much as the output. The losses in 
No. 8 are about one-half as great, so that it secures a saving of 
over 1100 k.w. hours per annum for a single 10 k.w. trans- 
former. | 

If the copper and iron losses at full load are known, the all- 
day.efficiency of any transformer is easily calculated, as shown in 
the table. The iron loss, being constant, is found for the whole 24 
hours, and the copper loss for the particular loads and periods of 
operation. The sum of these losses is added to the calculated out- 
put to give the input, and the former divided by the latter is the 
efficiency. 

Regulation in Transformers is the percentage of fall in second- 
ary voltage from no load to full.load for constant potential work- 
ing. The constant current transformer will be considered under 
that special heading. . The potential difference between the second- 
ary terminals is less at full load, than at no load, on non-inductive 
load being chiefly due to the resistance drop in both the primary 
and secondary coils. Calling /’ and /” the primary and secondary 
currents, A’ and &” the resistances of the primary and secondary 
coils, £’ and £” the primary and secondary £.//./s. respectively, 
being practically the terminal voltages measured at no _ load, 
we have 











/ / 
Percentage of resistance drop in primary = i = (73) 
: n IT 
é ee i «secondary = Fin (74) 
T&R! pits R!" 
Percentage of total resistance drop = Fil ita rad (75) 


If both numerator and denominator in (73) be multiplied by 


12, Pr 


I’ we have Fy Which is the percentage of primary copper loss in 


watts compared with total primary input in watts. The value of 


TRANSFORMERS. 165 


this latter fraction must be the same as that in (73), hence fhe 
percentage of copper loss in watts 1s the same as the percentage of 
resistance arop tn volts. Vhis applies to primary or secondary cir- . 
cuits and to total values. 

In addition to the drop due to resistance, the regulation or total 
fall in voltage is aggravated by the magnetic leakage at full load. 
In well-designed transformers, great care is taken to make this 
latter factor a minimum by arranging the coils and core as ex- 
plained in connection with Figs. 125 and 124. The result is that 
the diminution of secondary voltage caused by magnetic leakage is 
only about ten per cent of that due to resistance. Since the latter 
is usually from 1 to 8 per cent for large and small transformers 
respectively, the total fall in voltage, that is, the “regulation,” is 
.1 to .3 per cent greater. We have just seen that copper loss and 
resistance drop are equal percentages, hence the regulation may be 
considered as having about the same value, being only one-tenth 
greater in most practical instances. 

The resistance increases with the load on account of heating, 
the maximum allowable rise in temperature being 50°C. (Amer. Inst. 
Elec. Eng. Standard), which would augment the resistance about 20 
per cent. If full load is applied to a transformer, the resistance 
drop will increase about 20 per cent after a run sufficiently long to 
give the maximum temperature. Therefore the regulation and the 
copper loss when “hot” are about 20 per cent greater than when 
“cold.” Both values are often given, but the former is generally 
the proper one to consider, the other representing merely a tem- 
porary condition. In calculating efficiency, it has been shown on 
page 162 that this variation makes very little difference, since the 
losses are only partly due to resistance; but regulation is directly 
proportional to the latter, and any change in one produces a corre- 
sponding change in the other. : 

The time required for a transformer to reach maximum work- 
ing temperature depends upon its size and construction, being usu- 
ally between 6 and 18 hours. For this reason a transformer that 
_ operates at full load for shorter periods might properly have its - 
regulation and efficiency determined after an ordinary run. 

Although the regulation of transformers appears to be good, 
the drop at full load being only 1 to 3 per cent, nevertheless it is 
a serious difficulty in alternating current distribution. © This is 


166 KEE CTRICVIYGHTING. 


because it is in addition to variations in the generator, lines, etc., 
which occur on any electrical circuit. Even if hand or automatic 
regulation at the station counteracts any drop in the generator and 
lines, it is impossible to overcome the drop in each transformer, since 
one may be heavily, and another lightly, loaded on the same cir- 
cuit. Being about equal to the drop in the house wiring, it doubles 
the /oca/ fall in voltage. For example, a loss of 2 per cent in the 
wiring would not be very noticeable, but a variation of 4 per cent 
is objectionable. What is needed is some means of raising the 
secondary voltage automatically with increase of load, that is, 
something similar to compound winding in a generator. This 
might be made to compensate for the drop in the transformer, and 
in the wiring as well. Unfortunately no such device has yet been 
applied practically. The various methods of regulation employed 
for alternating current systems will be described in the next chap- 
ter, but none of them overcome this particular trouble. 

Another difficulty in this connection is the fact that the drop 
in a transformer is aggravated by inductive load. For example, a 
transformer which falls only 2 per cent in voltage at full non-induc- 
tive load, will have a drop of about 4 or 5 per cent with a full load 
having a power factor of 80 per cent. With lower power factors 
which often obtain in practice, the regulation would be still worse. 
Methods of Cooling Transformers. The total iron and copper 
losses, ordinarily amounting to 2 to 4 per cent, appear as heat in 
the core and coils; and since this production of heat goes on con- 
tinuously so long as a transformer is in operation, some means 
must be provided to prevent the temperature from rising above a 
certain safe limit. With small transformers their surface is rela- 
tively large compared with the heat produced, so that the latter is 
dissipated by radiation, conduction, and convection sufficiently fast 
to prevent excessive rise in temperature even for a continuous run 
at. full load: Y.In'darver transtommerspthe fossesmincreiseamnionc 
rapidly than the surface, so that some special means must be pro- 
vided for cooling them. These losses are by no means inconsider- 
able; a 100 k.w. transformer, for example, having about 2 k.w. 
loss, which is sufficient energy to supply forty 16 c.p. lamps. The 
more rapidly that heat is taken away from a transformer, the 
ereater may be its output without exceeding the allowable tempera- 
ture rise. In other words, smaller quantities of iron and copper 


TRANSFORMERS. 167 


are required for a given capacity in k.w. if effective means of 
cooling are provided. 


METHODS OF COOLING TRANSFORMERS. 


Self-cooling dry transformers. 

Self-cooling oil-filled transformers. 

Transformers cooled by forced current of air. 
Transformers cooled by forced current of water. 
Transformers cooled by combination of above means. 


A lA he 


Self-cooling ary transformers. It has just been explained that 
smaller sizes do not require any special means of cooling, since 
their surface is relatively large. Some larger types up to 50 k.w. 
are also made in this way; but, as stated above, they are heavier 
and more expensive than the following forms. | 

Self-cooling, otl-filled transformers are very generally employed, 
the entire core and coils being immersed in oil. ‘Transformers are 
practically always enclosed in a cast or sheet iron case, and this is 
simply filled with oil. No increase in cooling surface is thereby 
secured, but the natural circulation of the oil tends to equalize the 
temperature of the various parts, and carries the heat to the case 
from which it is dissipated. In most self-cooling types the case is 
made with external ribs or corrugations to increase its surface. 
The large volume of oil also absorbs considerable heat, so that the 
temperature rises more slowly; hence for moderate periods of opera- 
tion up to 3 or 4 hours, which is ordinarily sufficient in electric 
lighting, the maximum temperature would not be reached. An- 
other advantage gained by this arrangement is an improvement in 
insulation. This is due to the high insulating qualities of the oil 
itself, and to the fact that a disruptive discharge takes place 
through it much less readily than through the air that it displaces, 
distances being the same. It possesses, moreover, the power of 
self-repairing any break in the insulation. If ordinary materials, 
such as cloth or mica, become punctured, they lose their insulating 
properties, and the apparatus cannot be used until the fault is 
repaired, which ordinarily involves considerable time and expense. 
On the other hand, if oil is punctured, it tends to close in and 
repair the break, unless the discharge lasts so long that a charring 
occurs, which may make a permanent conducting path. 

The chief objection to the use of oil is the danger of fire. If 
a short-circuit occurs inside of the transformer, the oil may be 


168 ELECTRIC LIGHTING. 

thrown out and ignited at the same time, or a fire started in some 
other way might be made far more disastrous by the presence of 
a large quantity of oil. In this way several plants have been de- 
stroyed by fire with large loss of property. There is no special 
precaution that will entirely eliminate this risk ; but care in locating 
such transformers, in avoiding overheating, and in protecting them 
by effective lightning arresters, will reduce the hazard. 

Air-blast transformers are now commonly employed, and have 
the advantages over the oil-cooled type, that the danger of 
fire is avoided, and the cooling effect may be regulated in ac- 
cordance with the working conditions. They are so constructed 
that air can circulate through and around the core and coils, the 
ventilation being forced by a blower driven by a motor. A trans- 
former of 100 k.w. capacity requires about 850 cubic feet of air 
per minute at a pressure of .4 ounce per square inch, the power 
consumed being less than ,', of one per cent of the full-load out- 
put of the transformer. The flow of air is controlled by dampers, 
and the proper amount may be determined from its temperature 
as it issues from the top; ordinarily this should not be more than 
20° C. above that of the atmosphere. 

Water-cooled transformers are also oil-filled in most cases. A 
continuous flow of cool water is maintained through pipes im- 
mersed in the oil, through a water jacket formed in the casing, or 
through the conductors (primary or secondary) themselves if they 
are sufficiently large. It is the most effective method of cooling, 
and is very convenient for water-power plants, the supply and 
pressure being at hand. Where a natural flow is not available, 
pumps or the city water mains may be utilized. It is found that 
about 3 gallon of water per minute is sufficient for a 150 k.w. 
transformer. This type requires the least weight of iron and 
copper for a given output, since its heat is carried away most 
rapidly. 

Instead of having a flow of water, the oil itself may be drawn 
off, cooled, and then returned by means of a pump driven by a 
motor. In any of these types of transformers depending upon 

Pe forced circulation of air, water, or oil, it is vitally important to 
* avoid any stoppage of the flow, as it is likely to cause a burn-out. 

Phase Relations in Transformers. If /’ a certain alternating 

E..M.F. is impressed upon the primary coil of a transformer, a 


TRANSFORMERS. 169 


primary current 7’ flows, which’ sets up an alternating flux in the 
iron core. This in turn induces an alternating F.J/.F. in the 
secondary coil, which produces a current provided the secondary cir- 
cuit is closed. The secondary 4.1/7). £” is almost exactly opposite 
in phase to /’ the primary £.4/./“, as represented in Figs. 130 and 
131. If the secondary circuit is open, the primary current /’, 
which is then called the exciting current, lags behind £’ a certain 
amount, being usually about 45° as indicated. When the second- 
ary circuit is closed, and any current greater than one-tenth of full 
load flows in it, the primary current /’ is brought very nearly in 
phase with /’, so that the power factor is practically 100 per cent 
provided the secondary circuit is non-inductive; these conditions 


E’ 


360° 





E’ 


Figs. 130 and 131. Transformer Phase Relations. 


being shown in Figs. 182 and 133. The magnetization MW. (ie. 
alternating flux) in the core differs in phase by 90° from 4’ and 
also from ££”. In other words, the maximum flux occurs one- 
quarter period later than the maximum impressed /.17./. This 
is because the &.47.F. is zero when the flux is a maximum and 
does not vary (at 180° in Fig. 133); also the Z.A/F. is highest 
when variation of flux is most rapid (at 270° in Fig. 183). The 
magnetization is nearly constant for all loads, except that it de- 
creases slightly at heavy load, owing to magnetic leakage. Conse- 
quently the ratio of transformation (/":£”) is nearly constant, 
being practically equal to the ratio of the number of turns in the 
primary and secondary coils. For simplicity in the diagrams, £” 
is made one-half of /’,so that 7” would be about twice as great as 


170 ELECTRIC. LIGHTING. 


/’ since the secondary watts are almost equal to the primary watts, 
the efficiency being 96 to 98 per cent. In the primary circuit, 
besides the impressed 4.47.7, we have the “.AZF. of self-induc- 
tion and of mutual induction. With open secondary, there is no 
mutual induction, and the £.M/.F. of self-induction is opposed 
and nearly equal to the impressed £.17.F., so that very little 
current flows, usually only 1 to 3 per cent of full load. But 
when current is drawn in the secondary, the 4.4/7.7. of mutual 
induction rises and tends to neutralize the £.1/.F. of self-induction, 
so that the primary current increases proportionally. These con- 
stitute the main physical quantities involved in the action of a 
transformer; but in addition there are certain other factors which 





Figs. 182 and 133. Transformer Phase Relations. 


are smaller, but play parts of some importance. One of these is 
the magnetizing current which overcomes the reluctance of the 
core, /This lags 90° behind 2’ the impressed 2.7/7 ands 
therefore wattless. The current which supplies the core loss 
(hysteresis and eddy currents) is the other component of the excit- 
ing current /’ in Fig. 130. It is in phase with Z’, and represents 
real power. In practice these two components are usually about 
equal, producing approximately 45° lag with no load. 

The resistance drop in voltage in the primary and secondary 
coils (/’R’ and /’R”) are also small quantities which must be 
considered, since they affect the regulation as already explained 
under that head. The primary resistance drop is usually } to 1 
per cent of the primary £.J4/7./, and the same for the secondary. 


TRANSFORMERS. Veh 


Their effect at full load is to increase the apparent ratio of trans- 
formation as measured at the terminals, in practice producing a 
fall in secondary voltage corresponding to their sum. 

Magnetic leakage is still another small quantity that affects the 
action of a transformer. It interferes with the regulation by 
increasing the fall in secondary voltage usually about } per cent, 
with full non-inductive load as stated on page 165, and more than 
this, with inductive loads. Its effect is similar to that of inductance 
introduced in the primary circuit. 

Inductance tn the secondary circuit produces a lag of secondary 
current behind secondary £././.., the same 
as for other alternating current circuits, the 
angle being shown in Fig. 82. This pro- 
duces a corresponding lag in the primary 
circuit, so that the power factors of both are 
reduced, being equal to the cosine of the 
lag angle. The regulation is made much 
poorer by this condition, the drop in second- 
ary voltage being increased from 1 per cent 
with non-inductive load to 23 per cent with 
.90 power factor or 26° lag. In fact, this 
causes serious trouble when there are induc- 
tion motors or other inductive load on the 
same circuits with lights. 

Resistance drop with lagging current is 

Fig. 134. Transformer 
represented in Fig. 134, in which OA is the Phase Relations. 
useful portion of the impressed £.17.F., OB 
is the total £.47F. induced in the secondary coil, O/’ is the 
primary and O/” the secondary current, OF being the phase of the 
magnetization. The primary resistance drop /’X’ is in phase with 
the primary current 7’, and similarly 7” is in phase with 7”, hence 
the impressed E.M.F. is OE’, and the secondary E.I7F. is OE”, 
The ratio of transformation at no load is OA + OB, and at full 
load it 'is OH’ + OE”, which is considerably greater, so that the 
secondary voltage must fall if the impressed /.4Z.F. is constant. 

Constant Current Transformers. For the operation of arc or 
incandescent lamps on series circuits an approximately constant 
current is required. In direct current distribution this is produced 
by the Brush and other well-known types of self-regulating dyna- 





ee ELECTRICUMGHTING. 


mos. Corresponding machines have been designed for the alter- 
nating current, but it is a more common practice to obtain a con- 
stant alternating current from the secondary circuits of special 
forms of transformer, the primary circuits of which are supplied in 
parallel at constant potential. A prominent example is the Gen- 
eral Electric constant current transformer illustrated in Figs. 135 


‘ 
» 
: 
3 
i 
S: 
4 
x 
& 
* 
x 
% 
¥ 
x 





Fig. 135. Constant Current Transformer. 


and 136. In its simplest form, it consists of a core of the double 
magnetic circuit type with three vertical limbs, and two flat coils 
placed around the central limb. The lower coil, usually the pri- 
mary, is fixed, while the upper is suspended and balanced so that it 
can move up and down a considerable distance. The larger trans- 
formers have one fixed primary below, and another above with two 
secondary coils which are balanced on levers and move in opposite 


TRANSFORMERS. svg’ 


directions, as shown in Fig. 185. Very large sizes sometimes have 
four sets of coils with a single magnetic circuit. 

When currents flow in the primary and secondary coils, a repul- 
sion is produced between the coils, so that they tend to move away 
from each other. For a given secondary current (usually 6.6 
amperes for enclosed arcs), the repulsion is balanced by a certain 
weight, so that any increase in current due to cutting out of lamps 
in series causes the coils to separate, and wzce versa, thus automati- 
cally maintaining a nearly constant current. The quadrants on the 
levers are made adjustable, because the repulsion for a given cur- 
rent is not the same for all positions of the coils, being greater 
when they are close together. 
This enables the current to 
be kept almost exactly con- 
stant from one-third to full 
load, but in practice these 
transformers are usually ad- 
justed so that the current at 
half load is 10 per cent less 
than at full load. This is 
done because the wave form 


SS ———————— XX ——— KX 





Secondary. x 








S.P Switch, 






|_ Jt P Switch, 
of most alternators produces 
i 


(i eae 
an increase in voltage at the 1 
Main Line Primary. 


lamps when the constant cur- Fig. 136. Constant Current Transformer. 
rent transformer is working 
on light loads. The full-load efficiency varies from about 96.5 per 
cent for 100-light transformers to about 94.5 per cent for 25-light 
transformers. The whole apparatus is placed in an iron case with 
corrugations to increase the cooling surface, which is filled with 
oil in order to carry away the heat, increase the insulation, and 
serve as a dash-pot to prevent too rapid movement of the coils. 
These transformers will operate without much attention, and 
may be placed in the stations where the current is generated, in 
sub-stations, or, if specially designed, in manholes under the 
Streer 
Two 100-light transformers of this kind tested by Professor 
W. L. Robb and described by him in a paper on this subject * 
gave the following average results: 


* “Transact. Amer, Inst. Elec; Eng) September, 1899. 


174 ELECTRICHLICH LING. 


Loap. EFFICIENCY. Power Factor. 
One-quarter 88.1 per cent 24 per cent 
One-half OD Pee! 4 
Three-quarters 94,9.qitt a S68 eV UAE | on a 
Full 9671 Osan igen gee a 


The low power factor and efficiency at small loads make it un- 
desirable to operate these transformers below 70 or 80 per cent of 
their rated capacity. In street-lighting, for which they are most 
often used, the load is generally at least 80 or 90 per cent of the 
full amount, hence this objection does not apply. 

Other forms of constant current transformer have been designed 
by the Fort Wayne Company and others, the coils being station- 
ary, and the regulation being due entirely to magnetic leakage and 
resistance drop. In this case the leakage, which is most carefully 
avoided in constant potential 
transformers, is purposely ex- 
aggerated by the arrangement 
illustrated in Fig. 1387. Any 
rise of current in the secondary 
coil S tends to “blow out”’ the 
flux produced by the primary 
coil P, the magnetic leakage 





Fig. 137. Constant Current Transformer. across the air-gap G increasing 
at the same time. This tends 
to prevent the secondary current from varying, even though the 
resistance in the secondary circuit is altered considerably. In such 
a transformer the current does not rise more than 10 per cent 
when the load (i.e., number of lamps in series) is increased from 
one-quarter to full value. 
The methods of connecting and operating these transformers 
will be discussed in the next chapter. , 
_~~Protective Devices for Transformers. In almost all cases the 
primary and secondary circuits of transformers are designed to 
operate at widely different voltages. For electric lighting the 
ordinary primary pressure is about 2000 volts, and the secondary 
about 100 or 200 volts. In long distance transmission the higher 
pressure may be 10,000 to 30,000 volts, or even more. Evidently 
it is a very serious matter if, by failure of insulation or other cause, 
the high-voltage current breaks through to the low-voltage circuit. 
The latter is not, and in practice cannot be, sufficiently well. insu- 


TRANSFORMERS. LID 


lated to withstand the effects of the high pressure. Moreover, the 
danger to persons is very great, since the presence of the deadly 
current is likely to be entirely unexpected. There would be little 
object in using a transformer if the low-tension circuit had to be 
treated with the same precautions as the high-tension. In fact, 
this is a grave difficulty in the operation of transformers. The 
high-voltage may break or leak through to the low-voltage circuit, 
either on account of defective insulation between the primary and 
secondary coils inside of the transformer, or it may occur through 
accidental contact of the primary and secondary conductors out- 
side of the transformer. In either case the trouble is often due 
to, or developed by, hghtning or other atmospheric. electrical dis- 
charges. For this reason transformers working on overhead lines 
are more likely to have difficulties of this kind than those used 
‘in connection with underground wires. 

The principal means employed to avoid or mitigate the effects 
of interconnection between primary and secondary circuits of 
transformers are: 

1. Tests of insulation by manufacturer. 

Zoelsighining arresters: 

3. Devices for automatically grounding the secondary circuit 
when its pressure rises abnormally. 

4, Grounded metallic shield interposed between primary and 
secondary circuits. 

©). Permanent grounding of secondary circuit. 

6. Test wires run from the station to the secondary circuits of 
transformers. : 

7. Periodical testing of transformer insulation by extra high 
pressure to develop latent faults. 

8. Insulation tests of primary circuits of system. 

All transformers should be tested for insulation strength by 
their manufacturers. <A testing pressure at least twice the rated 
voltage, z.e., twice the higher voltage, should be applied for not less 
than one minute. Tests are made between the primary and the 
core or case, and between the primary and secondary coils. In very 
high-voltage transformers (10,000 to 20,000 volts) it is sufficient 
to connect at rated pressure first one and then the other terminal 
of the high-voltage winding to the core and to the low-voltage wind- 
ing. This subjects the insulation to twice the normal pressure. 


176 ELECTRICAIV OCH TING. 


Lightning Arresters are described in Vol. I. Chapter XXIV. 
In connection with transformers they are very important, as many 


of the cases of break-down of insulation are caused by atmos- 





OOOV 





— aa 
—=- —-=-FILMs 


GROUND 
Fig. 138. Automatic Grounding Device. 


pheric electricity. 

Lhe automatic grounding of 
the secondary circuit by abnor- 
mal rise in its voltage is accom- 
plished by various devices. One 
of these commonly used in Eng- 
land is the “ Cardew earthing- 
device}, «It. consistsioheiwvo 
horizontal brass plates,insulated 
and separated from one another 
by 3 inch of air space, the up- 
per being connected to the 
secondary circuit of the trans- 
former, and the lower being 
well grounded. A thin strip 


of aluminum foil is attached at one end to the lower plate and rests 
upon it. A lug on the upper plate approaches to within 4 inch 


of (thesireé:end of thes toil 
When the potential of the 
upper plate rises above 300 
volts, due to accidental con- 
nection with the primary, or 
Other Circuit ties oll siseat 
tracted upward electrostatic- 
ally, thereby making contact 
with the lug, and grounding 
the secondary circuit. This 
will in most cases blow the 
fuses in the primary circuit, 
and cut off the dangerous 
current. 

The film cut-out invented 
by Professor Elihu Thomson 


> 
o 
1e) 
ie) 









8TATIC BALANCE 
GROUNDING DEVICE 


GROUND 


Fig. 139. Automatic Grounding Device. 


is similar to the Cardew device, the difference being that thin paper 
or other insulating material is used in place of the air-gap. This is 
punctured by excessive voltage, and the secondary circuit is 


TRANSFORMERS. jens 


srounded, as is evident from Fig. 138. A similar automatic device 
is indicated in Fig. 139, the secondary being grounded when an 
electrostatic balance is caused to act by abnormal potential. It is 
not necessary that these or other devices should be connected to 
both wires of the secondary circuit, as in Figs. 138 and 139; one 
ground connection being sufficient, but two are less likely to fail. 
Another automatic means of ground- 
ing consists of an electromagnet in 


1OOOV} 


series with a vacuum tube between 
the secondary circuit and the ground. 
When the potential rises above a cer- 


tain value, it produces current enough =| MWY 
through the magnet to cause it to 
operate a mechanism that grounds 
the secondary circuit. 
All of these automatic grounding 


devices are open to the objections that er 
ig. 140. Transformer Protection. 
they do not act instantly, so that the | 
insulation might break down before they operated ; besides which 
they might fail because they depend upon contact points and 
mechanism. | 
A grounded metallic shield between primary and secondary 
coils is another form of protective device 
due to Professor Thomson. It is simply 
a covering of sheet metal, placed between 
the primary and secondary windings in 
such a manner that it is impossible for 
current to leap from one to the other 
without passing through the shield, which 
naturally leads it away to the ground 
(Fig. 140), thus protecting the low-ten- 
sion circuit. 


GROUNDED 
SHIELD 





1000V 





GROUND 
Fig. 141. Grounded Secondary The permanent grounding of the 


Circuit, : Sy Gee 3 : 
secondary circuit, indicated in Fig. 141, 


is perhaps the most positive means of protection, but is open 
to some objections. It was formerly forbidden by insurance 
rules in this country, but is now permitted. The ground connec- 
tion should be a very good one, similar to that required for light- 
ning arresters (Vol. I., p. 437), and the wire leading to it should 


178 ELECTRICODIGCHIING. 


have a current capacity fully equal to that of those portions of the 
primary and secondary circuits through which the current might 
pass to the ground. 

The objections to this arrangement are: 

1. Insurance authorities have opposed any grounding of strong 
current electric circuits used inside of buildings, because a single 
fault would then cause a short circuit or leak, whereas with com- 
pletely insulated circuits ¢zwo s¢multaneous faults are required. 

2. A permanent ground connection zzvzfes trouble, since with 
it a break-down in insulation between primary and See ee is 
more likely to occur than without it. 

8. Certain conditions may arise under which trouble will be 
aggravated by the ground connection. 

The first of the above objections 
is minimized by requiring the ground 
connection to be made at the neutral 
° 6 point of the secondary circuit. In case 

the latter is a three-wire system, this is 
the middle or neutral wire as represent- 
on edun bio alt 2 Wath alt wo-wireacecs 
= ondary circuit the middle point of the 
secondary coil may be grounded, a con- 


1000 
Vv 


Ere tee nection being brought out for the pur- 
Fig. 142. Secondary Circuit with ; : 
Ns a A) pose. By grounding the neutral point 


instead of one of the outer conductors, 
the voltage is divided in halves, so that the tendency to break down 
insulation is reduced in still greater proportion. 

The fact that the insulation between primary and secondary is: 
more likely to break down if the latter is grounded, is self-evident ; 
but it may be answered that the consequences are provided for, and 
the total danger is reduced. There are, however, certain possible 
conditions which might cause serious trouble on a grounded sec- 
ondary circuit. For example, an accidental connection between 
the primary and secondary circuits may allow the primary current 
to flow through the whole or part of the secondary coil. This will 
tend to produce an abnormally high voltage in the latter that may 
rise to several times the ordinary value, so that lamps, sockets, 
insulation, etc., will be burnt out. In order for this to take place 
the primary circuit must happen to have a ground connection on 


TRANSFORMERS. 179 


the side opposite to that on which the accidenta. contact with the 
secondary exists. It is necessary also that this last-named fault 
should be on the primary wires before they reach the transformer, 
otherwise the primary fuses would blow, and cut off the current 
entirely. In short, this combination of circumstances is ‘not likely 
to occur, and if it did the danger would be great whether the sec- 
ondary were grounded or not. 

Test wires may be run from the central station and connected 
to the secondary circuits of the various transformers. This per- 
mits the insulation resistance between each of the primary wires 
and the secondary circuits to be determined at the central station. 
In fact, a ground detector may be used which would instantly indi- 
cate a fault. A single test wire might be used; but it is better to 
divide the transformers into groups, each of which has its own wire, 
so that any trouble may be located more readily. These wires may 
be quite small. 

Pertodical tests of the insulation of each transformer should be 
made at least once a year. A small step-up transformer is carried 
to the places where the tests are to be made. Its secondary vol- 
tage should be at least twice the primary voltage of the system, and 
its current capacity at least four times the charging current that 
flows during any test. Its primary is connected to the high-voltage 
lines, and one terminal of its secondary is connected to the primary 
and the other to the secondary of the house transformer, which 
must be disconnected previously from both primary and secondary 
circuits. This pressure is applied for one minute, thus subjecting 
the insulation between the primary and secondary circuits to twice 
the working voltage, which is likely to develop any fault. A fuse is 
put in the circuit to protect it in case the insulation is punctured. 

Insulation tests of the primary circuit by means of ground 
detectors and special measurements are very important on systems 
using transformers, since any defect in the insulation of the latter 
will almost certainly lower the general insulation of the primary 
circuit, giving warning of some trouble. By keeping careful watch 
on the insulation, and promptly following up any indications, serious 
consequences may be avoided. This method differs. from the pre- 
ceding one in the fact that no test wires are required. 

Transformer Fuse Blocks or Cut-outs. To protect transformers 
from excessive currents, fuses are inserted in the primary circuit. 


180 ELECTRIC LIGHTING. 


The boxes or blocks which contain these fuses may be attached to 
or combined with the transformer as illustrated in Fig. 128, or they 
may be entirely separate from it as shown in Fig. 143. In either 
case the fuse itself is usually inclosed in or carried by a tube or 
plug of porcelain which is easily inserted and withdrawn through a 
hole in the box in order to facilitate the inspection or renewal of a 
fuse. Fuse-blocks are made either double- or single-pole as repre- 
sented in the two illustrations cited. The presence of a fuse in 
the primary circuit protects the secondary circuit also, since an 
abnormal current in the latter causes a corresponding increase in 
the primary current which will blow the fuse and open the circuit. 





Fig. 143. Transformer Cut-outs. 


In most cases the secondary circuit is further protected by fuses 
inserted in the local or house wiring. 

Testing Transformers. For determining efficzency various 
methods have been employed. That used by Professor Ryan * con- 
sisted in tracing out by means of instantaneous contacts the curves 
of primary and secondary /.4/.F. and of primary current, the sec- 
ondary current being measured by an ammeter. Having obtained 
these curves, the power in each circuit was calculated, and the ratio 
gave the efficiency. This method also has the advantage that the 
exact form and phase relations of the several waves are brought 


* Trans. Amer. Inst. Elec. Eng., Dec., 1889, 


TRANSFORMERS. 181 


out. Mr. W. Mordey * proposed to find the efficiency of a trans- 
former by running it at the given load until a constant temperature 
is reached as determined by a thermometer or by a resistance test. 
Direct currents are then passed through the coils of such strength 
that their heating effect maintains the same constant temperature. 
It follows that the direct current power (= /2R=£J), which is 
easily measured by volt- and ampere-meters or by a watt-meter, 
must be equal to the total losses with the alternating current. 
Calorimetric methods have been used by Dr. L. Duncan, + the total 
losses being determined by placing the transformer in a water, oil, 
or*ice calorimeter. Both of these last methods, depending upon 
heat measurements, are laborious and liable to error. . 

Volt- and ampere-meters may be employed to measure the pres- 
sures and currents in the primary and secondary circuits. If the 
load is non-inductive and more than one-tenth of full value the pro- 
duct of secondary volts and amperes, divided by the product of pri- 
mary volts and amperes, is the efficiency. With very light load or 
with inductive load the current lags behind the £.4/-F., and the 
voltamperes must be multiplied by the power factor (cos ¢) to get 
the true watts. By means of one of the various three-instrument 
methods, the true power can be determined; but the simplest plan 
is to measure the true watts in the primary and in the secondary 
circuits with wattmeters. 

Stray power methods are convenient and accurate, the losses 
being determined individually. The iron losses, which we have 
seen are constant (page 154), are determined by a wattmeter in the 
primary circuit when the secondary is open. The copper losses 
may be calculated for any load by (69) if the primary and second- 
ary currents as well as resistances are known or can be measured, 
which is usually an easy matter. Since the efficiency is always 
found for a definite load, the secondary current is fixed by that 
fact. The primary current /’ is 


ieee ee (76) 


in which /” is the secondary current, & the ratio of transformation, 
and /, the exciting current which flows with open secondary. If 


* Jour. Inst. Elec. Eng., London, vol. XVIII. p. 608. 
+ Electrical World, vol. IX. p. 188. 


182 ELECTRIC LICHLIING. 


/, is assumed to be 3 per cent of /” + & the error in the efficiency 
will be very slight. Having determined the iron and copper losses 
the efficiency is equal to the secondary watts divided by the second- 
ary watts plus the losses as given by (72). 

Potential Transformers are used to furnish current for volt- 
meters or wattmeters. They are small transformers (Fig. 144), 
usually mounted on the switchboard, their function being to con- 
vert high voltages to lower values that are more convenient and 
safer to measure. With 
a definite ratio of trans- 
formation, a volt- or watt- 
meter supplied from the 
low-voltage secondary 
circuit, can be calibrated 
to indicate the original or 
primary voltage. If the 
currents consumed _pro- 





iB duce a certain percentage 
ecient ee ae | of drop in the secondary 
voltage a corresponding 
error 1s introduced, un- 
less the instrument is 
specially calibrated to 
allow for this. A simpler 
plan is to use a trans- 
former having sufficient 
capacity so that the drop 
is insignificant. One should not connect additional instruments or 
pilot lamps to a potential transformer until it has been ascertained 
_ that they do not cause an objectionable fall in secondary voltage. 
~— Auto-Transformers. In these devices the primary and second- 
ary currents both flow in a single winding. The circuits of one 
form of auto-transformer are represented in Fig. 145, A & being 
a coil of insulated wire wound upon an iron core as in an ordinary 
transformer. When the coil ABZ is supplied with alternating cur- 
rent from the primary circuit on the left, differences of potential 
are established between the various parts of the coil. If connec- 
tions are made to it at the points Cand JP, which divide it into 
three equal parts, the potential difference between D and £ will 





Fig. 144. Potential Transformer. 


TRANSFORMERS. 183 


be one-third of the total voltage applied at A and BZ, and between 
C £ it will be two-thirds of that value. Assuming, for example, that 
300 volts are supplied at A and 4, then 100 volts may be tapped 
off from D and — and 200 volts between Cand £. 

These might be used in almost exactly the same way as the 
common types of transformer with separate primary and secondary 
circuits, since a certain number of watts at one voltage may be 
converted into a nearly equal number of watts at another voltage. 

There is an objection, however, to auto-transformers, arising 
from the fact that the secondary is connected directly to the pri- 
mary circuit, as at B and £ in Fig. 145. Although the actual vol- 
tage between the secondary wires may not be high, nevertheless 
conditions may arise that will make the secondary 
circuits very dangerous. For example, an acci- 
dental ground anywhere on the primary conductor 
A will subject to the full primary voltage a per- € 
son who is connected to the earth and happens to 


touch the secondary wire &. It is practically the 
same as if the primary current breaks through to 3 = 
the secondary circuit in an ordinary transformer, Fig. 145. 


and we have seen in Figs. 188 to 142 what pre-  — Auto-Transformer. 
cautions are taken to make this danger as small 
as possible. On this account auto-transformers are not suitable for 
general use on high-tension systems. They are employed chiefly 
for series circuits in electric lighting, as described under that head 
in the next chapter. They are used also in place of dead resistance 
for starting alternating current motors. It is evident that they 
may be applied as compensators to subdivide the voltage in three- 
and five-wire systems instead of the machines described on page 79. 
The action of an auto-transformer is similar to that of the ordi- 
nary transformer. In either case the primary current sets up an 
alternating magnetic flux which induces an F.//.F. in each turn of 
winding. In an auto-transformer there is only one winding; but if 
any two points,as D and £& in Fig. 145, are connected to a suitable 
circuit, a current will flow through it. This tends to produce a 
demagnetizing effect similar to that due to the secondary current 
of the common transformer; hence the primary current increases, 
in order to maintain the same magnetization, and automatically 
adjusts itself to supply the energy drawn in the secondary circuit. 


184 ELECTRIC LIGHTING. 

Reactive and choke coils, which are somewhat similar in con- 
struction and action, will be described as means of regulation in the 
next chapter. 

Standard Types of Transformers. The following table gives 
data concerning standard commercial transformers of from .6 to 
50 k.w. capacity. It will be noted that the 125 cycle type has 
less core loss, and higher efficiency, but poorer regulation, than 
the 60 cycle type; the differences, however, are not very great. 


GENERAL ELECTRIC TYPE H OIL TRANSFORMERS. 
ADAPTED FOR USE ON 50 to 140 Cycle Circuits. 


Data Based on 1040 or 2080 Volts Primary and 60 Cycles (Column A), or 125 Cycles (Column B). 


EFFICIENCY. 





Watts 
Capacity. 
Core Loss, 
Watts. 

Full Load 
Copper Loss, 
Watts. 
Regulation, 
Per Cent 
Quarters 
Load. 
Quarter 
Load. 


One- 


Three- 
One- 
Half- 
Load 








600 
1,000 
1,500 
2.000 
2.500 


Ca 
— 
- 


=> 


CROSS 





CO Oo OC 
CO ec CO 


taest 


~~ 








amd we 
eS i en) 
OOO OO 
Se Ng aici 
S Ob eo 
cc TO 
em OTTO bh 
OO ee 
Pore 
Co OO CO 
SOS ae ates) 
He © Os © OO 
ve) co © 
ERM Sp 
me or © Or 
Cc 
SERS ae 
Onoon 
eave) 
OOH BRa 


ve) 
¢ 
coe 


3,000 
4.000 
5,000 
7,500 
10,000 


co <O 


RR co IS 
Wonoan 
CO OHO OH 

DAIAAHD KRAGRER ONONSrAy 


B 
4. 
5. 
5. 
5. 
6. 
6. 
6. 


SH SO 


— 


— 
re 
COS005 ocome- 


WAIN TW 
OO OO 
BRAAS 
CO ~1 Ca > bo 
OO 6 6 
SINS 

wmowonn 
aire mvelvelive) 
DRAAAS 
OADPPeH 
OO 6 tO 20 
SINT SIS OD 
wWwreHoon 
He bO bc oH 
OO 0 0 
Se ess) 
SOc O69 


© 6 
Hs bo G9 00 bo 


st 
+] 
OOO Oe 








15,000 
20,000 
25,000 
30,000) § 
40,000 
50,000 














TA -1 


=—j 
= . 








SSS S13 3 C3 Sa Ov Oxy Ox 


N44 
Or O1 09 bS CO 


IO ont to Ht 


CO 2 CO CO CO CO 
Ps ES NG NS ES 


SScaoo 
OO OH OH OO 
CO 8 OH CO CO CO 
NOWOOR HU 
OD OH OO CO 
SS ie eae ae 
OOO CO ~1r 
COO OO C29 
See shoe es ee 
C CO CO AI OS CO 
COCO Oo OO 
PHD HOT 
mt OCH Or 
OOo mo 6 
OTH CO Te 











Temperature rise not exceeding 45° C. for A and 40° C, for B in 8 hoars full load. 

Temperature determined by increase of resistance method. 

For comparison with data based on 1000 or 2000 volts primary, deduct 7% from the above core loss 
and add 0.1 to the per cent regulation. 

The above transformers are suitable for operation on circuits having voltage within 10% above or 
below the rating. 


Polyphase Transformers. Exactly the same types of  trans- 
formers as those used‘ for single-phase currents may be employed 
with two- and three-phase currents, each phase or branch having 
its own transformer or set of transformers. It is possible, -also, to 


construct special polyphase transformers in which the magnetic 
circuits are combined in a manner analogous to that in which the 


TRANSFORMERS. 185 


electric circuits are interconnected, as explained with reference to 
Fig. 115. In this way a certain saving in the material of the iron 
core is effected; but they are more complicated in construction than 
ordinary transformers, and are seldom used in this country. A 
description of them may be found in Jackson’s Alternating Currents, 
page 683. The arrangement and operation of transformers in 
connection with polyphase systems will be described in the next 
chapter. 

For further information regarding the theory, construction, and 
operation of transformers reference may be made to the following 
works : 

The Alternate Current Transformer, by J. A. Fleming, new 
edition, 2 vols. N. Y. and London, 1896. 

Alternating Current Phenomena, by C. P. Steinmetz, N. Y., 
LSTAG) 

Alternating Currents, by D.C. and J. P. Jackson, N. Y. and 
London, 1896. 

The Principles of the Transformer, by F. Bedell, N. Y. and 
London, 1896. 


CEUAE Tike x 
ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 


THE facility with which alternating currents may be trans- 
formed from one voltage to another gives possibilities of variation 
in systems of distribution that are greater than with direct cur- 
rents. Adding to this the transformation from two- to three-phase, 
and from alternating to direct currents, or vice versa, by rectifiers 
and rotary converters, and the opportunity for elaboration becomes 
almost unlimited. There has been a tendency to yield to this 
temptation, and go too far in the complication of circuits and appa- 
ratus. Certain systems have become more or less standardized 
and generally accepted, but alternating current practice is still far 
less definite than direct current work. The more important meth- 
ods will be classified and described in the present chapter. 

Alternating Current Series Systems. — Series circuits  corre- 
sponding to the direct current arrangements shown in Chapter II. 
may be operated by alternating currents. The principal systems 
that have been used are — 

1. Simple series circuit with constant current alternator. 

2. Series circuits supplied by constant current transformers. 

3. Parallel-series circuits. 

Several forms of constant current alternators have been intro- 
duced, analogous to the well-known Brush and Thomson-Houston 
series arc dynamos, the principal example being the Stanley ma- 
chine made by the Westinghouse Company. No regulating device 
is required to keep the current constant; but armature reaction and 
self-induction are purposely exaggerated in the design, so that the 
current does not increase very much, even when the machine is 
short-circuited. The same is true to a certain extent of a constant 
direct current dynamo, but self-induction has a much greater effect 
with alternating currents. On the other hand, the voltage of a 

186 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 18T 


constant current alternator rises very high if the circuit is opened, 
since it is entirely relieved of armature reaction and inductance 
drop. This is likely to break down insulation unless it is pre- 
vented by providing a film cut-out similar to that shown on page 
25, or some other device connected to the terminals of the ma- 
chines, so that it will short-circuit the latter if the voltage becomes 
too great. Such machines have no advantage over constant direct 
current dynamos, except that the main current is generated with- 
out a commutator; but they require some source of direct current 
for field excitation. Furthermore, there are many examples of 
the direct current type that are very successful, hence they are gen- 
erally adopted for arc-lighting on a simple series circuit, the direct 
current lamp being preferred when other considerations are equal. 

Constant current transformers have been illustrated in Figs. 








Fig. 146. Constant Current Transformer System. 


135, 136, and 137, and their operation described. They are not 
used on a true series system, since their primaries P are supplied 
in parallel at constant potential, as represented in Fig. 146, the 
secondary circuits S only being arranged in series fashion, and car- 
rying constant currents which feed the lamps L.- The advantage 
of this method is the fact that a large number of lights can be 
operated from the same source of current. For example, each of 
the circuits: in 2,/,G, Fig. 146,.may have as many lamps as an 
entire dynamo in the direct current series system; so that one 
large alternator of 1000 k.w. capacity’ can supply about 2000 
lights ; whereas it would require 16 to 20 direct current machines, 
since the number of lamps that can be fed by a single dynamo is 
usually limited to 100 or 125. In simplicity and in economy of 
operation the single large alternator would have considerable ad- 
Valitave-s ees transformers“ 7)</), 7, may,,bew ole diferent sizes, if 


188 ELECTRIC LIGHTING. 

desired, being used to supply a larger or smaller number of lights. 
Lamps may also be cut out of circuit, as at / and 4K, the current 
being kept constant by the transformer in each case ; but the latter 
may be designed or adjusted to maintain in one circuit a different 
value from that in the others. The primary circuits’? are fed by 
the mains J/7V, with constant voltage from the alternator A ; hence 
the current in each primary is nearly proportional to the watts 
in the secondary. In other words, it increases as lamps are added 
in: series. - On the other hand, the ‘current 1s constant in each 
secondary circuit, and the voltage automatically rises as the number 
of lamps is increased. ‘Thus we have the interesting case of a con- 
stant potential primary and a constant current secondary circuit. 
This is made possible by the fact that the flux through the secon- 
dary coils varies with the load, whereas it is practically unchanged 
in the ordinary transformer. Hence the core loss is not a constant 
in the former, but the copper loss is always the same in the secon- 
dary coil, and increases in the primary circuit as the square of the 
load. The last fact is true of a constant potential transformer, but 
the first two do not apply to it. 

Parallel-series systems are often operated by alternating cur-— 
rents, being analogous to the direct current circuits shown on page 
26. Like the latter, they are used chiefly for street-lighting with 
series incandescent lamps. The general arrangement is similar to 
that represented in Fig. 9, one source of current being used to 
feed several circuits in parallel. Hence all are supplied with the 
same voltage, introducing difficulties when lamps burn out, or 
when it is desired to run different numbers of lamps on the various 
circuits. One plan consists in switching in extra or “relief” 
lamps Z, as is done with the direct current system described on 
page 26. But the alternating current has an advantage over the 
latter in this respect, as it may be regulated by reactive coils, or 
auto-transformers (Fig. 145), which are more efficient and conve- 
ngent than resistance coils or lamps. Several such methods have 
been used, in one of which variable reactive coils are placed in 
series with each circuit, and any reduction in the number of 
lamps is compensated by increasing the reactance drop in the coil. 
In another arrangement each lamp Z is shunted with a reactive 
coil C, as illustrated in Fig. 147. These coils consume very little 
real power, but they have a certain potential difference across their 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 189 


terminals, thus feeding the lamps. When one of the latter burns 
out the continuity of the circuit is maintained, the current flowing 
through the coil, which also consumes about the same voltage as 
before. But as this last condition is only approximately fulfilled, it 
is necessary to have ad- 
ditional reactive coils & 
in each circuit to regu- 
late the current. 

The so-called CR 
regulator, made by the 
General Electric Com- 
pany, is another means 
of operating series in- 





candescent lamps. It 


Fig. 147. Alternating Current Series System. 


consists of an auto- 

transformer, the connections of which are shown in Fig. 148. 
The primary coil A/’B, and the coils BZ and CV, are all wound 
upon the same iron core. When a plug is inserted in the con- 
tacts at R, and the switch arms // and G are in the position 
indicated, the voltage of the supply circuit from the switchboard 


| From Switchboard 





Secondary 


Fig. 148. Regulator for Alternating Current Series Systems, 


is decreased by the opposing /.M./. produced in the portion of 
the coil CD included between.the arms #7 and G. If the po- 
sition of the latter is reversed, then the primary voltage is in- 
creased by the same amount. Thus the whole or part of the 


190 ELECTRIC LIGHTING. 


coil CD may be made to raise or lower the primary £.J7.F. by 
moving the arms’ GH. Transferring the plug from R to S in- 
creases the primary £.J17.F. by the voltage produced in the coil 
BE; and on changing the plug to P, the primary 4.4/./. is dimin- 
ished by that due to the coil #4. This secures a wide range of 
regulation ; for example, the primary AZ is wound for 2200 volts, 
FB and BE being each wound for 430, while CD produces 230 
volts in steps of 23. With a plug at P, the secondary gives 2200 
— 430= 1770 volts, with the arms G and AH in the middle; and 
by moving the latter the voltage may be varied from 1540 to 
2000. Changing the plug connection to A, the regulation is from 
1970 to 2430, and putting it in S, the range is from 2400 to 2860 
volts, the total variation being’ 1540 to 2860. These regulators 
are also wound-for 1100 volts, giving a range in secondary voltage 
from 440 to. 1760. The secondary current is either 3.5 or 5.5 
amperes, lamps designed for this current being connected in series, 
but only the two ends of -the circuit are shown in Fig. 148. Sev- 
‘eral circuits, each with its own regulator, are connected to the same 
source “of alternating current in a manner similar to that repre- 
sented in Fig. 146. Each circuit is provided with an ammeter, and 
the attendant regulates the current by moving the switch arms 
GH, when it is too high or too low. The lamps take about 1 volt 
per candle-power at 3.5 amperes, and are arranged with automatic 
cut-outs, which short-circuit them if they break, as explained on 
page 26. 

Alternating Current Parallel Systems. The simple arrange- 
ment of lamps in parallel on a two-wire circuit may be supplied by 
an alternator without transformers, being analogous to the ordi- 
nary direct current system represented on page 28. This method, 
however, is rarely used for electric lighting alone, since the direct 
current has generally been adopted in such cases, including the 
majority of isolated or other plants in which the distances are not 
great. For the operation of motors, polyphase parallel systems 
are often used with or without transformation of voltage; and lamps 
are supplied from the same circuits or generators, but they are not 
intended primarily for electric lighting. The single-phase current 
is not well adapted to the running of motors for general purposes, 
this being the principal objection to it. It is only when the vol- 
tage is to be transformed up or down that the single-phase has any 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 191 


special advantage over the direct current system, hence it is seldom 
used without transformers. But there is nothing to prevent the 
installation of two- or three-wire systems similar to those illustrated 
on pages 28 and 70, the direct current dynamos being replaced by 
alternators of equivalent voltage-and current capacity. In fact, 
such plants have been installed in a few instances. 

Single-phase parallel systems with transformers. This is the 
most common method of distribution with alternating currents. 
One alternator A (Fig. 149), or two or more alternators A and B 
working in parallel, supply current to the bus-bars UV, from which 
the lines J7V and RS convey current to the primary circuits P of 
the various transformers .7;- Lhe lamps Z are connected in paral- 
lel to thessecondary circuits S of the transformers. ‘The latter 
operate at approximately constant potential in both primary and 


UV 





rasan Uae 





D S P Coke ees Y AL 


Fig. 149. Constant Potential Transformer System. 


secondary circuits, being of the ordinary type that has been fully — 
discussed in the preceding chapter. In most cases the alternatorg, : 


generate about 1100 or 2200 volts, which is carried with a loss of 


about 10 per cent by the conductors AZM, so that the primary coils © | 


of the transformers 7 receive about 1,000 or 2,000 volts, which .is) 
transformed down to about 100 volts for supplying the lamps Z on 


the secondary circuits. Formerly a secondary voltage of 52 was 


generally employed, but at present 104 volts has become the stand- 
ard in alternating current practice. This change reduces the 
weight of copper in the secondary wiring to one-quarter with the 
same percentage of drop. There isa tendency to economize still 
further in the secondary conductors by adopting lamps of 220 or 
208 volts, or by using the three-wire system as described in the 
following paragraph. 

Lhree-wire Alternating Current Systems. As already stated, 


i a 


192 ELECTRICGLIGHTING. 


- 


two- or three-wire parallel circuits may be supplied by single-phase 
generators without transformers, but they are seldom used. The 
two- and three-phase systems may also be operated with three 
wires, and will be described later. The system here referred to 
corresponds to the ordinary direct current three-wire circuits set 
forth on page 70, except that it is supplied from the secondary 
coils of transformers. When the alternating current was first in- 
troduced for electric lighting the secondary circuits and lamps were 
generally operated at 52 volts, a transformer being placed in or 
near each house to be lighted. But it was found that the lower 
efficiency and greater core-loss of a number of small transformers 
gave results far less economical than those obtained by the use of 
fewer transformers of larger size. This naturally requires that the 
average lengths of the secondary circuits should be increased ; and 


fiom Ts | z = 
een a 





Figs. 150 and 151. Three-wire Single-phase Systems. 


in order to avoid excessive cost in the latter, 104-volt lamps have 
become the standard in alternating current installations. The next 
step in this direction is the adoption of the three-wire system for 
the secondary circuits. This is easily arranged either by employ- 
ing two transformers as represented in Fig. 150, or by using a 
transformer with two equal secondary coils as in Fig. 151. In 
both cases the primary is an ordinary two-wire circuit, all the. 
primary coils being connected in parallel ; but each pair of second- 
ary coils are put in series, the neutral wire / being led from the 
intermediate point B. The wz/zke terminals must be connected at 
B in order to give double voltage between the outside wires A and 
C. If the like terminals are united at B the two sides will be in 
parallel, and.the middle wire / must carry the sum of, instead of 
the difference between, the currents on the outer conductors, as 
explained on page 82. 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 198 


A two- or three-wire network of conductors, similar to the direct 
current systems described in Chapter VI., is often adopted for alter- 
nating current distribution. A transformer 7, or a bank of trans- 
formers, is placed at each feeding-point, the primary coils being 
supplied from the station generators A £# by the high-voltage con- 
ductors & -*G H, and the secondary coils being connected to the 
low-tension mains composing the network VA7. These transform- 
ers are located in sub-stations or in manholes in the street. The 
lamps LZ are fed from the network as indicated in Fig. 152. In 
this case a two-wire network is shown; but a three-wire system 
similar to that represented in Fig. T4 is also used in many places, 


the transformers being connected in the manner shown in Figs. 150 _/% 
— 


and 151. 
Regulation of Constant-Potential Alternating Current Systems. 
Nearly all of the methods of regulating the voltage of direct cur- 





Fig. 152. Network supplied by Transformers. 


rent systems described on pages 51 to 69 are applicable to alter- 
nating current circuits. For example, the potential of an alter- 
nator may be controlled by varying its field current, using the 
ordinary rheostat operated by hand. In this way the voltage of the 
generator may be kept constant or may be increased a certain 
amount with rising load to make up for the drop in lines and trans- 
formers. This drop is greater for alternating than for direct cur- 
rents on account of reactance, and the falling off in potential of 
alternators is also larger at full load than with dynamos. 

Composite Wound Alternators. Tomake an alternator automa- 
tically maintain a constant, or a rising voltage with increase of load, 
it is provided with compostte winding analogous to the compound 
winding of direct current machines. 

In order that a generator may be self-regulating, the current 
which it produces is caused to act upon the field-magnets in order 


194 ELECTRIC LIGHTING. 


to increase their strength in proportion to the current generated. 
Since an alternating current cannot be used directly for exciting 
the field-magnets it is necessary to rectify it forthe purpose. One 
method is indicated in Fig. 153, the coils CC being the ordinary field 
winding supplied by the separate exciter /, and producing most of 
the magnetization. The composite coils DD are also wound upon 
the field-cores, and are fed through the rectifying commutator 
FR, which is mounted upon the same shaft as the armature AA, 
but to avoid confusion is represented on one side in the dia- 
gram. The commutator & has as many segments as there are 
poles, alternate segments being connected to one terminal Z 
of the armature winding, and the intermediate segments being 
connected to one of the lines JZ by the wire W, and brush 


SHON 





Fig. 1538. Composite-wound Alternator. 


on the collecting-ring at /. The other terminal S of the arma- 
ture winding is connected to the second collecting-ring G. The 
collecting-rings /'G are also mounted upon the shaft in the usual 
manner. With this arrangement, the connections of the composite 
coils D are reversed at the brushes / and XK each time that the 
armature current reverses, so that a unidirectional flow is estab- 
lished through these coils. This tends to augment the magnetiza- 
tion of the field as the load increases, the effect being the same as 
that of compound winding. It is necessary that the brushes / and 
kK should be set carefully, so that each passes from one segment 
to the next at the same instant that the current reverses. In this 
way sparking is avoided since the current is zero at that moment. 
A shunt shown inside of the commutator # in the diagram, and 
moving with it, is sometimes used when it is desired to rectify 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 195 


only a portion of the current. A stationary shunt Q is generally 
employed to regulate the current in the coils DY, thus giving a 
means of adjusting the amount of compounding. 

In most cases the current produced by an alternator is of high 
potential, so that it is not desirable to introduce a commutator in the 
main circuit or to pass this current through the field-coils. To avoid 
these objections, the main current is carried through the primary 
coil of a small transformer, the secondary of which is connected to 
the segments of the commutator A, and is wound to give a low vol- 
tage. The latter is therefore directly proportional to the main cur- 
rent, and produces through the brushes / and A a magnetizing 
current in the composite coils YD that increases with the load. 
This transformer is usually placed inside of the armature. Instead 
of putting a composite coil DY on each field core, as represented in 
Fig. 153, they are sometimes concentrated upon one or two of the 
field cores. If the two halves of the armature winding are in 
parallel, composite coils must be put on at least two poles; and 
these must have symmetrical positions, otherwise the £.47./. in 
the two armature circuits will be unbalanced. 

The above-described forms of composite-wound alternators do 
not regulate properly for inductive as well as non-inductive loads, 
but the General Electric Company build compensated field alter- 
nators designed to adjust automatically the voltage for all varia- 
tions in load or lag. This machine is described in the American 
Electrician, Nov., 1899, and Elec. Review (N.Y.), May 28, 1900. 

The automatic constant-potential regulator described on page 
57 is used for alternating as well as direct current systems. The 
arrangement employed for the former is fully illustrated and de- 
scribed inthe American Electrician of October, 1899, p. 488. An- 
other arrangement of this kind, made by Ganz & Company of Buda- 
Pesth, is described in the work on Alternating Currents by D. C. 
and J. P. Jackson, page 313. It consists essentially of a solenoid 
connected as a high-resistance shunt to the main circuit, and con- 
trolling a number of contact points dipping in mercury, thus vary- 
ing the resistance in the field circuit. 

Feeder Regulation. The various methods of regulating direct 
current feeders described on pages 61 to 69 are applicable with 
slight modification to alternating current distribution. It is evi- 
dent, for example, that the introduction of non-inductive resistance 


196 PLECTRICWUILTEING. 


in any circuit will produce a drop in voltage equal to the product 
of the current and resistance. Hence, the regulation of feeders 
by means of rheostats, as described on page 64, is practically the 
same for alternating as for direct currents. In addition to this 
the effect of self-induction may be utilized to produce a drop in vol- 
tage if desired. On page 125 it was shown that the drop due to in- 
ductance alone is 27/Z/ and that due to resistance and inductance - 
combined is /VR2 + (27fL)2. In practice selfinduction coils are 
often employed to control alternating currents, and they possess 
the advantages over resistance coils that they are more compact, 
and consume much less actual energy for the same drop, but they 





cause the current to lag. Various names are applied to them, 
such as reactance coils, impedance coils, and choke coils. By sub- 
dividing them, and leading out connections to contact points, the 
effect may be varied as in the case of an ordinary rheostat. 

Feeder Regulation by Variable Ratio Transformers is a very con- 
venient method in alternating current distribution. They take the 
place of the “boosters” (page 67) used in direct current systems. 
It would be possible to vary the potential of a feeder by means of 
an auxiliary alternating current machine put in series with it, and 
acting either as a generator or motor to raise or lower the voltage. 
But a transformer being simpler, cheaper, and more easily taken 
care of, is generally used to accomplish the same results. There 
are several such devices in common use, a prominent example 
being the Stillwell Regulator, made by the Westinghouse Company, 
and represented in Fig. 154. It consists of a primary coil, which 
is connected in shunt, and a secondary coil in series with the main 
circuit. By means of a movable switch arm, more or less of the 
secondary winding may be introduced into the circuit, thus “ boost- 
ing’’ by a corresponding amount the voltage of the generator. A 
switch is provided to reverse the connections of the primary coil, 
so that the secondary potential may be added to or subtracted from 
that of the alternator, thus doubling the range of regulation. 
Assuming that the secondary coil is wound for 100 amperes and 
100 volts, and that the alternator generates 2100 volts, the circuit 
will be supplied at 2200 volts, when all of the secondary winding 
is inserted so as to raise the pressure the full amount. By moving 
the switch arm to the left, part of the secondary is cut out, and the ~ 
voltage is reduced until it becomes 2100, when the arm is at zero. 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 197 


On reversing the primary coil by the lower switch, and then mov- 
ing the arm of the upper switch to the right, the opposing AZ. 
set up in the secondary winding reduces the pressure of the feeder, 
until finally it becomes 2000 volts. In this way any value between 
2000 and 2200 volts may be obtained. When the secondary is 
adding 100 volts to the generator’s potential, it is producing 10,000 


LINE | 


wor rn nr ee A ee ee ee ee 


Bai 


REY $90 Pa Be ae meee se 


CONTACTS 


FACE PLATE 


PINGS 


PREVENTIVE 
SPESISTANCE 






SECONDARY Core 


SUVMIAR Y COWS 





PIEVER SING Swi7ctH 


a mew we + ee + ee eee ee =e 






Fig. 154, Internal Connections of Stillwell! Regulator. 


watts with a current of 100 amperes. Under those circumstances 
it will draw 2100 volts, and about 5 amperes, or about 10,500 
watts, from the alternator; the difference being the various losses 
in the transformer, which would have an efficiency of about 95 per 
cent. If the primary is reversed in order to reduce the voltage, 
about 95 per cent of the energy is returned to the circuit. Hence 
the actual loss is small in any case, being only about 25 X ay5=ab0, 





198 ELECTRIC LIGHTING. 


= 


or 44% at maximum or minimum voltage, and less than that at inter- 
mediate values. Regulators are required when two or more feed- 
ers are to be operated at different potentials. If there is only one 
circuit, or if <all the feeders 
are supplied with the same 
voltage, the regulation may 
be accomplished by varying 
the field of the alternators 
by means of rheostats. But 
when one feeder demands a 
different pressure from the 
others, then each should be 





Ke provided with its own regu- 
Fig. 155. Principle of Feeder Regulator. ; : 

lator, allowing independent 

control according to the load, distance, and other conditions. 
Another type of feeder regulator: made by the General Electric 
Company is represented in Fig. 156. The principle of its action 
is shown diagrammatically in Fig. 155, PQ being the primary coil 
of many turns of fine 
wire connected across 
the main conductors 
AB, coming from the 
altermatone ahaa 2 
being the secondary 
coil of a few turns of 
heavy wire connected 
in series with one of 
the main conductors 
at J Kee ee laminated 
IDO (sCOnEG We uaa s 
mounted within the 
primary and second- 





ary coils, and is capa- 
ble of being turned Fig. 156. Feeder Regulator with Cover Removed. 

into the position GAH, 

indicated by dotted lines. When the core is vertical, the mag- 
netic lines produced in it by the primary coil PQ, set up a cer- 
tain £ J/.F. in the secondary coil S7, and we assume that this 
aids the #.4/.F. of the generator. If, now, the core be turned 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 199 


to the position GH, then the direction of the lines of force are 
reversed with respect to the secondary coil, so that an oppos- 
Inve .27./0 willsbesproguced, » I husiibysturningsthe core, the 
potential difference between the line wires C and D may be raised 
above or reduced below that of the generator conductors A and 4. 
This device has the advantage of being free from sliding contacts, 
the regulation being obtained by shifting or reversing the flux, and 
the variation is perfectly gradual—not in abrupt steps. The 
actual construction is illustrated in Fig. 156, both coils with their 
terminals being clearly seen. A ring of laminated iron (not shown 
in either cut) surrounds the coils and core, in order to improve the 
magnetic circuit ; and all the parts are inclosed in a cast-iron case, 
which may be filled with oil for cooling and insulating purposes. 
The core is turned by means of the hand wheel shown in Fig. 156. 
These regulators may be 
used also for dimming 
lights in a theater, as con- 
trollers for series lighting 
instead of the arrangement 
shown in Fig. 148, or to 
adjust the voltage on the 
branches of an unbalanced 
polyphase, or three-wire single-phase system. 

Compensators for Voltmeters. In order to determine the volt- 
age at the outer end of a feeder, it is necessary to run special 
‘pressure wires”’ from the station to the given point, or to use a 
compensated voltmeter, as explained on page 64. With alternating 
currents, the latter method is much more difficult to apply than 
with direct currents, because the compensator must allow for both 
ohmic and inductive drops, and must be correct, whether the cur- 
rent lags or leads with respect to the £.J/.F. These conditions 
are fulfilled by the Wershon compensator, made by the Westing- 
house Company, and represented in Fig. 157. The generator G 
supplies the lamps Z, through the feeders 47M. The ordinary 
potential transformer C is used to reduce the pressure for the volt- 
meter VJ7; and an inductance A, as well as an ohmic resistance B, 
are inserted in series with one main conductor. ‘The drop due to 
A and B& is introduced into the voltmeter circuit by two small trans- 
formers £ and J, the iron core upon which the inductance A is 





Fig. 157. Mershon Compensator for Voltmeter. 





200 EDE GARI AGAIING. 


wound being used as the core of the transformer £, of which the 
coil A is the primary. With this arrangement C gives to the volt- 
meter a pressure proportional to that of the generator ; while 
introduces into the voltmeter circuit an opposing £.J/./’. propor- 
tional to and in step with the inductive drop on the line, and D 
produces another opposing /£.J/./’. proportional to the ohmic drop 
on the line. The result is that the voltmeter indicates the voltage 
at the distant end of the line or feeder. The plan here shown is 
commonly employed, but various modifications are possible. 

Polyphase Systems. The principles of two- and three-phase 
circuits have been shown in Figs. 110 to 121, and will enable us 
now to consider their application in systems of distribution. As 
already stated, a two-phase circuit is practically equivalent to two 
single-phase circuits, and each may be considered separately. In 
fact, in most cases they are used separately for electric lighting, as 
represented in Fig. 111; and even when the two circuits have a 
common return conductor in order to save one of the four wires 
(lig. 112), the conditions are practically the same as for single- 
phase distribution, except that the common conductor C carries a 
current 1.41 times greater than that in B or &, as explained in 
connection with Fig. 113. ge 

For isolated plants or central stations supplying polyphase 
current at moderate distances transformers are not required; and 
the lamps, motors, etc., may be connected directly to the circuits, 
as indicated in Figs. 111, 112, 115, and 117. In such cases the 
pressure may be about 110 or 220 volts, which is suitable for incan- 
descent lighting and for constant potential are lighting, the lamps 
being connected singly or two in series. Either the two- or three- 
phase systems are often adopted where the operation of motors is 
an important part of the service. For example, in many cotton mills 
the looms and other machinery are run by polyphase induction 
motors, and it is convenient to feed the lamps from the same gen- 
erators. It is generally preterable, however, to employ separate 
circuits for lighting and power in order to avoid the objectionable 
effect of the latter upon the former due to the sudden and large 
increase in current occurring when motors are started. This diff- 
culty is almost always met with if motors and incandescent lamps 
are supplied by the same circuits; but it is usually more serious 
with alternating than with direct currents, because most types of 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 201 


alternating current motors require a heavy current, usually lag- 
ging considerably, when starting. This not only causes a large 
drop on the line, but also reacts injuriously upon the regulation 
of transformers and generators, their voltage falling much more 
than with an equal non-inductive load. __ 

When the distances become considerable, that is, more than 
two or three miles, it is customary to employ pressures of about 
1000 or 2000 volts or higher, to economize in the conductors, and 
for long distance trans- 
mission of 50 miles or 
more 380,000 to 40,000 
volts are employed. In 
any of these cases, trans- 
formers are required to 
reduce the high voltage 
for transmission to low 





Fig. 158. Two-phase Circuit with Transformers. 


voltage for actual use in the lamps. Special polyphase transform- 
ers may be employed; but in most cases, especially in America, 
ordinary types the same as those designed for single-phase systems 
are adopted for polyphase work. 

For two-phase circuits the connections are very simple, as 
shown in Fig. 158, being precisely similar to the single-phase 
arrangement. The primary of each transformer 7 is connected to 
the main conductors &F of one phase or to G// of the other phase, 
the lamps Z being fed by 
the secondary circuits S. 
The generator 41s © an 
ordinary two-phase alter- 
nator. Any number of 





Fig. 159. Two-phase Circuit with Transformers. transformers pet be Le 

plied from either or both 
circuits “and GH up to their full capacity, there being no neces- 
sity for preserving a balance between them. If a two-phase motor 
is to be operated, it is connected to the secondaries of two trans- 
formers, one of which has its primary supplied from the circuit of 
one phase, and the other having its primary supplied by the circuit 
of the other phase, thus producing a two-phase current in the 
motor. If a single return conductor is used for both circuits, the 


transformers are connected as represented in Fig. 159, the wire F 


202 ELECTRIGULGIALING: 


od 


being common to both circuits. The secondary circuits of trans- 
formers on polyphase systems may be arranged for three-wire dis- 
tribution in the same manner as the single-phase circuits in Figs. 
150 and 151. All that is necessary is to use two transformers in 
series or to subdivide the secondary of each transformer. It is 
evident also that two-wire or three-wire networks similar to that 
illustrated in Fig. 152 may be supplied with polyphase currents. 
On ae -phase circuits transformers may be connected either 
| in Y or in A fashion as indi- 
cated in Figs. 160 and 161 
respectively. In the former 
case, three transformers have 
one terminal of their primary 
circuits brought to a common 
or neutral point P, or a fourth 
conductor may be provided, as in Fig. 115, in order to connect 
these neutral points together. With the A arrangement (Fig. 





Fig. 160. Three-phase Y Circuit with Transformers. 


161) the primary of each transformer is connected between two of 
the three main wires, and the loads on the three branches must be 
closely balanced, otherwise their voltages will not be equal. The 
same is true of the three-wire Y circuit ; but the addition of a fourth 
or neutral conductor renders it unnecessary to maintain a balance 
provided the armature of the 
generator has a Y winding, 
the neutral point of which 
is connected by means of 
this fourth wire to one pri- 





mary terminal of every trans- 


Fig. 161. Three-phase A Circuit with Transformers. 


former. This last arrange- 
ment is the best one for supplying lamps by three-phase currents, 
but is not needed for motors, since the latter are connected to all 
three conductors, and draw current from them equally. 

In the three-phase systems already shown (Figs. 160 and 161) 
the secondary circuits are used separately, but if desired they may 
be connected according to the Y or the A plan. By varying their 
arrangement, a considerable range of voltage may be secured with- 
out any change in thetransformers. For example, assume that the 
pressure between any two of the main wires of a three-phase sys- 
tem is 1000 volts as represented in Fig. 162. Using three ordi- 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 203 


nary single-phase transformers, the primary of each is connected 
across two of the outside wires in A fashion; AZ being one primary, 
AC another, and SC the third. If the ratio of transformation is 
10:1, the voltage in each secondary coil will be 100 volts; and if 
these are also connected in A, then the voltage between any two 
secondary conductors, such as a and ¢, will be 100 volts. Keeping 
the primary circuits as before, but changing the arrangement of the 
secondary coils from A to Y, the voltage between the secondary lines 
becomes 173 volts in Fig. 163 ; since each coil, such as Ag, gener- 
ates 100 volts as before, but there are now two in series, so that 
the resultant pressure is V3 x 100 = 178 volts, as shown in Fig. 
118. By changing the primary coils to Y connection, the pressure 





OOO 





Figs. 162, 163, 164, and 165. Connection of Transformers on Three-phase Circuits 


for each coil WZ in Fig. 164 is 1000 + V3 = 580 volts, conse- 
quently the voltage between the secondary lines is only 58 volts. 
When both primary and secondary coils are Y connected (in Fig. 
165) the ratio of transformation is 10:1, as in Fig. 162, and the 
pressure between secondary lines is 100 volts. In this way sec- 
ondary voltages in the ratio of 100 :173:58 may be obtained from 
the same supply conductors without changing the transformers 
except in their external connections. 

The manner of arranging lamps upon a three-phase circuit is 
illustrated in Fig. 166, in which AD, BD, and CD represent re- 
spectively the coils of a three-phase generator or of three trans- 
formers with Y connection. Each group of lamps, such as QR, is 
connected between one main conductor CG, and the neutral point 


204 ELECTRICOLIGIALING. 


HT. If the three circuits feed equal numbers of lamps, as indicated 
at R, S, and 7, it would not be necessary to have the neutral wire 
Df; but if they are not balanced, as at V, Y, and WV, which is more 
likely in practice, the neutral wire is required in order to maintain 
equal voltages on the three branches. In that case the neutral 
carries the difference between the currents, so that lamps may 
be turned on or off without materially affecting the others, pro- 
vided the conductors are of sufficient size to avoid any of excessive 
drop. 

The regulation of polyphase systems may be effected by placing 
in series with each feeder an ordinary single-phase regulator simi- 
lar to those illustrated in Figs. 154-156. For two-phase circuits a 
regulator should be put in each phase, as, for example, in £/ and 
in Gf7in Fig. 158. A three-phase system should have a regulator 





Fig. 166. Lamps on Three-phase Circuit. 


in each of the three phases A, B, and C in Fig. 160. The use of 
independent regulators would enable the voltage to be adjusted 
separately in case the system is unbalanced, by reason of having 
differences in load on the three phases. With perfectly balanced 
loads, such as are produced by motors or by equal distribution of 
lamps, the three regulators should be adjusted alike, which may be 
accomplished by connecting them together mechanically. 

A simpler plan for polyphase circuits is to employ the so-called 
enduction potential regulator shown in Fig. 167, which controls the 
phases at the same time. It comprises a primary and a secondary 
winding, the former connected in shunt and the latter in series 
with the circuit. The &.4/.F. generated in each phase of the sec- 
ondary winding is constant; but by varying the relative positions 
of the two windings, this voltage may be added or opposed to the 
pressure of the circuit at any phase angle, so that the range of 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 205 


regulation is from maximum “boosting ’”’ to maximum lowering. 
The principle is somewhat similar to that of the single-phase regu- 
lator in Fig. 155. The movable core may be rotated by means of 
a hand wheel, or when it is desired to operate it from a distance 
the apparatus is fitted, in addition to the usual hand wheel, with 
a small motor arranged to turn the core by means of gearing, as 
shown in Fig. 167. This motor may be of the direct current or 
induction type, and is controlled by a reversing switch mounted 
on the switchboard or at any convenient point. 





Fig. 167. Induction Potential Regulator. 


Induction Booster. — Another means of regulating the voltage 
in polyphase systems consists in connecting in series with the 
feeder to be regulated or compounded, the field magnet coils (z.c., 
primary) of a small induction generator. For this purpose a ma- 
chine similar to an ordinary two- or three-phase induction motor 
may be employed, but it must be driven by an engine or motor at 
a speed somewhat above that of synchronism. If no current is 
nassing on the feeder, there will be no current induced in the 
armature of the machine, and no action whatever. But, as soon 


206 ELECTRIC. LIGHGING. 


as the current begins to flow in the feeder, it will induce current 
in the armature of the induction generator, which will react 
automatically on the field currents to add to their voltage. At 
any given speed above synchronism the boosting action depends in 
amount on the strength of the current in the feeder, while the 
action may be regulated by varying the speed at which the 
machine is driven. This evidently allows the main generator to 
be compounded or over-compounded without the use of sliding 
contacts, commutators or other objectionable apparatus, and also 
allows each feeder to be compounded separately, if desired, and all 
the feeders to be supplied from a single source of current. 


Generator Armarure 


Teazer Co/l 





Series Field 







‘Rectityin 
eG 


ere 


(a Feeder 


S__ 60 Teazer Wire 
ome = PI SOS ne a 
Q 160 Feeder 


Fig. 168. Monocyclie Generator Connections. 


we” The Monocyclic System. — The single-phase system is the sim- 


plest and best alternating current method when arc or incandescent 
lights are to be supplied, but no large number of motors, except 
perhaps, small fan motors, are to be operated. On the other hand, 
the polyphase systems are adapted to cases in which motors play 
an important part. The monocyclic system is a compromise be- 
tween the two, being adopted for installations which supply lights 
for the most part, but are required also to operate motors. The 
lights are supplied from the main armature winding, which is prac- 
tically the same as that of an ordinary single-phase generator. In 
addition to this main winding, the armature is provided with an- 
other set of coils, one terminal of which is connected to the middle 


207 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 


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PPP PPO? | | 


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REED (By eae A 
TTR | 
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4070OLU UbY 
4ozesuadwoy|- 
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208 | ELECTRIC LIGHTING. 

point of the main winding, the other terminal being led to a third 
collector ring, as represented in Fig. 168. The auxiliary winding, 
called the “teazer coil,” is so placed with respect to the other that 
they produce #.M/.F.’s, differing by 90° in phase, and they are 
designed to give 520 and 2080 volts respectively. From the prin- 
ciples explained on page 126, it is evident that the £.J7./., between 
the outer terminal of the teazer coil and either main terminal, is 
equal to V(1040)? + 520? = 1160 volts. The main current is passed 
through a rectifying commutator to feed the series field coils, and 
produce a compounding effect similar to that in the single-phase 





composite-wound generator shown in Fig. 153. 

The manner of supplying arc and incandescent lamps as well 
as motors by means of the monocyclic system is illustrated dia- 
grammatically in Fig. 169. It will be observed that all the lights 
and small single-phase fan motors are supplied through transformers, 
the primaries of which are connected to the two outer or main con- 
ductors only. In other words, they are fed with ordinary single-phase 
current. The large motors may be of either the induction or syn- 
chronous types and are supplied through two transformers, con- 
nected, as shown, to all three conductors, so that they receive, in 
addition to the main current, another current differing in phase 
from the former, which enables them to be started up as polyphase 


motors. 
For lighting purposes the usual forms of single-phase trans- 


formers are employed. In connection with motors the transform- 
ers may be specially designed for the mono- 
G E F cyclic circuit, or a pair of simple single-phase 
transformers may be arranged as indicated 
in Fig. 170. In the latter case the primary 
P q coils P and Qare connected to the three sup- 
ply conductors A, 4, and Cas shown, C being 
the auxiliary wire. The secondary coils S 
and 7 are connected in a similar manner, 
except that one of them is reversed, and the 
\ motor is fed by the three wires G, £, and F. 
Polyphase Transmission and Direct Current Distribution. — An 
‘important use of the polyphase system in connection with electric 
\\ lighting is for the transmission of energy at high potential from 
A \' the generating plant to sub-stations, where it is converted into 


S ay 


A C B 


Fig. 179. Transformers on 
'  Monocyc.ie Circuit. 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 209 


low-tension direct current for local distribution. The object of 
this plan, which has been adopted by many of the largest electric 
light and railway companies, is to combine the advantages of both 
alternating and direct currents. The essential features of this 
system are indicated in Fig. 171. The generators GG are gen- 
erally three-phase, since the conductors for this system require 
only three-quarters as much copper as for the two-phase system, 
the distance of transmission, voltage, percentage of drop and other 
conditions being the same. It is customary to employ a low fre- 
quency of 25 periods per second. ‘This is rather too low for 
satisfactory arc or incandescent lighting; but the energy is con- 





Fig. 171. Three-phase Transmission and Direct Current Distribution, 


verted or rectified into direct current or the frequency may be 
raised by means of a “frequency change” before it is used for 
feeding lamps, so that this objection is avoided. On the other hand, 
the low frequency is better for transmission, because the effects of 
inductance and capacity are less, and, moreover, it facilitates the 
operation of the generators in parallel, which is the usual practice 
in such installations. In the United States a standard voltage of 
6600 has been adopted, being considered to be as high a pressure 
as it 1s practicable to handle in machines, underground conductors, 
switches, fuses, circuit breakers, etc. This pressure is produced 
directly by the generators without step-up transformers, thus 


210 ELECTRIC LIGHIING. 


saving the cost of, space occupied by, and losses in, the latter. 
Motors are also operated directly at this voltage in order to drive 
arc-lighting dynamos or other apparatus. 

The generators GG are connected in parallel to the bus bars, 
B, B, B, through switches and oil circuit breakers (Fig. 172) or 
fuses CC. Means are also provided for bringing each machine 
into synchronism with those already running, before it is connected 
to the main bus bars, the usual indicating lamp or other device 
being employed for the purpose. The field magnets of all the 
generators are supplied in parallel from a set of direct current ex- 
citers, HZ, in the ordinary manner. It is well to have a storage 
battery in parallel with the exciters in order to increase the relia- 
bility of the field excitation. The strengths of the fields and 
therefore F.J/.F.’s of the generators are independently regulated 
by means of a rheostat, #, placed in each field circuit, which may 
be operated electrically. 

From the main bus bars, feeders /F lead out through oil circuit 
breakers or fuses, 2, and run to the sub-station or stations from 
which the energy is to be distributed. The drop on the feeders. 
is either 5 or 10 per cent, giving 6300 or 6000 volts at the sub- 
station. These feeders are usually underground cables of the 
form described in the chapter on Underground Conductors. After 
the feeders enter the sub-station, they again pass through fuses 
or oil circuit breakers, AA, and then to the high tension bus bars, 
FfHfH, from which the primary circuits of the static transformers, 
S, are supplied through oil circuit breakers, 2Z. In these trans- 
formers the energy is stepped down from 63800 or 6000 to about 
165 volts, and is then fed into rotary converters, A, which change 
it into direct current at about 270 volts. 

The ratio of conversion from single- or two-phase to direct cur- 
rent is 1: V2 =1:1.41, since the latter corresponds to the maxi- 
mum, value of the former (p. 114). The three-phase 4.4/,F. is 
V3 + 2 times that of a single-phase E.J7.F. obtained from the 
same rotary converter (p. 145). Hence the ratio of conversion 
from three-phase to direct current is V3 -+ 2: V2 = .613:1 
= 1:1.63 with a sine wave of £.JZF,, and is not capable of much 
change, as stated on page 97. On account of the latter fact, the 
regulation of the direct current voltage is effected by means of 
induction regulators / of the form shown in Fig. 167 inserted in 


ALA ERNATING CORRENI SYSTEMS OF (DISTRIB CTION. 211 


the secondary circuits of the stepdown transformers S. These 
regulators are capable of raising or lowering by 30: volts, or about 
10 per cent, the pressure produced by the rotary converters, 
which is 270 volts, hence the range of regulation is from 240 to 
300 volts. Each rotary, &, of 1000 k.w. capacity is provided with 
its own regulator rated at about 130 k.w. The static transformers, 
PS, of 3850 k.w. capacity each, are connected in groups of three 
with no cross connections between the groups on the secondary 
side ; z.e., there are no low-tension alternating current bus bars. 
Each group of three transformers feeds one rotary converter, to 
which the secondaries of the group are directly wired, there being 
no means of switching any rotary from one to another group of 
transformers. This arrangement is adopted to avoid the use of 
switches in the low-tension, heavy current alternating circuits, as 
well as to avoid the transference of stray direct currents from one 
rotary converter to another through the alternating current connec- 
tions, which transference is likely to take place when two or more 
rotaries are electrically connected to the same low-tension alternat- 
ing current bus bars. 

In most cases the rotary converters are operated as sz1-phase 
machines. The purpose of this arrangement is to reduce the 
copper losses in the rotary armatures, and consequently raise the 
capacity of the rotaries with the same temperature rise. As 
rotary converters have no field distortion their capacity is deter- 
mined solely by their heating lmit and their commutating ability, 
so that any means of reducing the heating correspondingly in- 
creases the number of kilowatts which a given machine will con- 
vert, provided there is sufficient field strength to reverse the cur- 
rents in the armature coils as their commutator segments pass 
under the brushes. It has been shown * that a machine which 
will deliver 100 kilowatts without overheating when driven 
mechanically as a generator, will deliver 131 kilowatts with the 
same temperature rise when run as a three-phase rotary converter, 
and will deliver 194 kilowatts when run as a six-phase rotary con- 
verter, other conditions remaining the same. This is allowing for 
the internal losses of the converter, and assuming that the im- 
pressed £.17.F. isin phase with the counter £.4/7./. of the 
machine. If wattless currents are not carefully balanced out, or 


* Steinmetz, The Evlectrical World, Dec. 17, 1898. 


O12 ELECTRIC LIGHTING. 


are used for purposes of regulation, the output of the machine with 
either number of phases falls off somewhat, but the six phases 
still show about the same advantage over the three phases. As- 
suming a wattless component amounting to 30 per cent of the 
total alternating current input of the machine, the same 100-k.w. 
generator would deliver 122 kilowatts as a three-phase rotary and 
167 as a six-phase rotary. In addition to the reduction of the 
heating, the six-phase arrangement distributes the heating much 
more uniformly around the armature of the rotary than do three 
phases, with which the heating is rather badly concentrated in a 
few coils. 

While the term “six-phase”’ conveys an idea of considerable 
complexity, it requires but very little modification of the usual 
three-phase arrangement. The generators and high-tension trans- 
mission lines are three-phase, the six phases being derived from 
the step-down transformers, which are of the usual single-phase 
type, and three in number, but have each two electrically indepen- 
dent secondaries. These six secondaries of the step-down trans- 
formers are connected in two separate A arrangements, one 
secondary of each transformer being reversed with respect to the 
other, thus producing currents differing 180° in phase. The con- 
nections of the three transformers are shown in Fig. 171, the 
primaries P being fed from the high-tension three-phase circuit 
arranged in A, the potential being either 6300 or 6000 volts, de- 
pending upon whether a drop of 5 or 10 per cent occurs on the 
feeders. Special taps are led from the primary coil to enable 
either voltage to be used. Each transformer has two secondaries 
which are connected in double A fashion, as represented, to give 
six-phase currents at about 165 volts which are carried through the 
induction regulator /. From the latter the six-phase energy passes 
to the rotary converter, & in which it is changed to direct current 
energy at about 270 volts. This energy is supplied to the outer 
bus bars J7 and 7; from which it is distributed through feeders VV 
to the ordinary three-wire network of conductors similar to that 
described on page 103. The drop on the feeders, .mains and house- 
wiring reduces the potential to about 230 volts, so that the lamps 
receive about 115 volts on each side of the system. 

Storage batteries are commonly employed in connection with 
these systems, being placed in the sub-stations, and charged from 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 


213 


the direct current side of the rotary connectors as represented 


pieeieine ioe bis 
tial for the three-wire system, _ 
and enable a more uniform 
load to be maintained on the 
generating plant, feeders, 
transformers, converters, etc., 
or allow them to be _ shut 
down temporarily... It affords 
also a means of starting up 
the rotary converters from 
their direct current sides. 
The Ole a 
somewhat different distribut- 


connections 


ing plant are shown in Fig. 
173, which represents the ar- 


rangement at the North 


Avenue Sub-station of the , 


Chicago Edison Company. 
In this case two three-phase 
rotary converters of 100 k.w. 
each are used, and the primary 
pressure is 4500 volts ; other- 
wise the installation is similar 
to that described in connec- 
tion with Fig. 171. 
- Substantially the same 
system of three-phase trans- 
mission and direct current 
distribution is employed for 
electric railways, the only im- 
portant differences being the 
facts that the direct current 
is produced 550 or 600 volts 
and the distribution is by two- 
wire instead of by three-wire 
circuits. 

In spite of the step-down . 
transformation and the con- 


Contact 


The batteries serve to subdivide the poten- 


f 









Pneumatic. 
Cylinder 








=~ 
LN 


bia _| Laminated 


Copper 
Contact 


Contact _- 
~Rods 





a 
Insulating 
—Sleeves - 





-Oil) Filled 
Cy| linders 
A > 


Porcelain 
-; Insulators 


Lifting Table 











-Lifting Cam 

















1] 
4 





Ze 


aa 
idddigp bitdig 





EZ 
14 
F 





SS a —— —} 
Fig. 172. Oil Circuit Breakers. 





214 ELECTRICMUIGHTING. 


on US 2 











FIELD &.P.D.T. SWITCHES 















1000 FIELD S.P2D.7% 


400 AMP. SWITCH 1 oO AMP. SwiTCHES [2% SWITCHES 
n 


409 AMP. SWITCH 1 





1000 ave 


SWITCHES 7 Z " r 
Oz: 5 
STARTING BOX 


SHUNT 
, 1000000 C.M. 


ASBESTOS CABLE 





vad: 
Ll} 100 K.W. ABC 
a ROTARY 


1000000 C.M. 
ASBESTOS CABLE 


1000000 C.M. 4000000 C.M. 
ASBESTOS CABLE ASBESTOS CABLE 


1000 AMP.SWITCHES 1000 AMP.SWITCHES 
benny 34S) SYNCHRONIZING LAMPS 
LAMPS mmog C) O 
000000 C.M 1000000 C.M. 
Sees bee a) A.C. AMMETER ASBESTOS CABLE A.C. AMMETER 
Se 


SERIES TRANSFORMER SERIES TRANSFORMER 


le O 
OIL COOLED REGULATOR OIL COOLEO REGULATOR 
209 P50 


1000000 C.M. | 


"LEAD COVERED CABLE 
1000000 C.M. 


Bitiens LEAD COVERED CABLE 


= 750000 C.M. 
te LEAD COVERED CABLE 


Sarie ae { 
Al g80 K.W' OIL COOLED 





TRANSFORMERS 
«— — -4500—_> 
uw 
pm) 
(3) 
=< 
(} 
> 
co 
e 
o 
oO 
ui 
oO 
+ 
fe} 
z 
| HIGH TENSION FUGES: 
wi 
=) 
o 
<= 
(3) 
> TO GROUND 
2 . 
i=) 
: von 
esr LIGHTNING ARRESTERS 
Wi 
(a) 
<= 
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Fig. 173. Connections at Sub-station. 


version from direct to alternating current, the efficiency of these 
systems is fairly high. The following figures have actually been 
obtained in practice.* The step-down transformers had an efficiency 


* Street Railway Journal, October, 1899, p. 710. 


a 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 215 


of 98.2 per cent at full load of 350 k.w. each, and the rotary con- 
verters of 990 k.w. each gave 96 per cent efficiency at full load, 
making a combined efficiency of 94.2 per cent. In comparing this 
with a system using alternating current throughout, it should be re- 
membered that the latter would require two sets of transformers to 
bring down the pressure from 6600 volts to that used in the lamps. 
In other words, a set of static transformers would be substituted for 
the rotary converters, so that the combined efficiency would be 
U3s20x 98/2" 96.4 instead of 94.2 percent. On the other hand, 
it would not be possible to use direct current arc lamps or motors, 
storage batteries, or any electrolytic apparatus in connection with 
a purely alternating current system. Furthermore, losses and the 
difficulties of regulation, etc., caused by inductance, capacity, and 
low-power factor would occur with alternating current in the dis- 
tributing conductors and house-wiring. In most practical cases 
these would more than offset the additional loss of 2.2 per cent in 
the rotary converters. 

A form of oil circuit-breaker used in the very high-tension 
(6600 volts) circuits of this system is illustrated in Fig. 172. It 
consists of a magnet operating the valve of a pneumatic cylinder 
the piston of which raises or lowers a metal cross-head carrying 
three wooden rods that extend down into three cells, each contain- 
ing the switching apparatus for one phase of the circuit. A _ sec- 
tion through one of these cells is shown in Fig. 172, the others 
being the same, and separated from each other by 4-inch brick par- 
titions to act as barriers and prevent arcing between the switches. 
The actual circuit-breaking parts are connected to the movable rods 
and are submerged in oil. This type of circuit-breaker is rated at 
10,900 volts and 800 amperes per phase. 

In connection with the above-described system of three-phase 
transmission and direct current distribution, it is common practice 
to employ double current generators, rectifiers, and frequency 
changers, which will now be explained under their respective 
headings. 

Double Current Generators. — Since a rotary converter is pro- 
vided with a direct current commutator and with alternating cur- 
rent collecting rings connected to its armature winding (page 
97), it may be employed as a generator if driven by an engine 
or other source of power, and polyphase or direct currents or 


216 ELECTRICALIGUTING. 


- 


both may be obtained from it. In some plants these machines 
are used as converters at one time and as generators at other 
times. They may be run as polyphase generators to supply 
energy at a distance through step-up transformers, and can also be 
utilized to charge storage batteries with direct current, these two 
functions being performed at different hours of the day or at the 
same time, if desired. When so used they are termed double cur- 
rent generators. The use of these machines in the stations of the 
Chicago Edison Company is described in The Electrical World and 
Lngineer, May 19, 1900, which also contains complete illustrations 
and description of the three-phase transmission and direct current 
distribution system employed ona very large scale by that com- 
pany. 

Rectifiers. — This name is given to.those forms of apparatus in 
which single or polyphase alternating currents are changed into 
direct currents by means of commutators; these machines being 
without field magnets or armatures. This distinguishes them from 
rotary converters which are complete dynamo machines.  Recti- 
fiers are much simpler, cheaper, and more efficient than converters; 
_ nevertheless, they have not been very generally introduced, chiefly 
on account of practical difficulties in keeping them in adjustment 
and avoiding sparking. 

In principle a rectifier is a reversing commutator Cin Fig. 174, 
similar to that of an open-coil arc dynamo (Vol. I. p. 382). In 





Fig. 174. Rectifier of Alternating Currents. 


this case a two-part commutator is represented, one segment being 
continuously connected to one wire J7 and the other segment to 
the other wire VV of the supply circuit. These connections are 
not shown, but are made through a pair of brushes and rings 
connected respectively to the two commutator segments. The 
wires (7 N lead from a single-phase generator G through a con- 
stant current transformer 7, and it is evident that the connections 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 217 


of the brushes A B will be reversed at every half revolution of the 
commutator. If a circuit feeding arc lamps Z in series be con- 
nected to brushes A #, it is evident that the current will flow 
through the lamps always in the same direction, provided the 
connections are reversed exactly when the alternating current 
reverses. In Fig. 175 the alternating current 4, B,C, D,F, etc., is 
converted into the pulsating direct current 4, B,C, £,F, etc., if the 
Leversals occur ate theapoints: ©, 2: 7; 


etc. It should be noted also that the 2 E S 2 
current is zero at the instant of re- ee Ns 
versal, hence sparking is avoided. In A 1K 


order that the action shall take place 
correctly the commutator C must re- ae = 
volve synchronously and in proper Fig. 175. Rectified Single-phase 
phase with the alternating current. ha 

For a two-part commutator the number of revolutions per second 
must equal the frequency, and the brushes 44 must be set very 
carefully so that they pass from one commutator segment to an- 
other at the instant when the current is zero. 

The constant current transformer 7 may be one of the forms 
already shown in Figs. 185, 186, and 137; and it will feed the 
lamps practically the same as if they were connected to it directly, 
except that the current through them will be unidirectional instead 
of alternating, thus allowing ordinary types of direct current arc 
lamps to be used. The fact that the current is pulsatory is not 
objectionable for arc lighting, since the standard Brush and Thom- 
son-Houston arc dynamos produce currents of this character. 
Incandescent lamps may also be operated equally well with this 
current. A low frequency of 25 is too low for very satisfactory 
running of either kind of lamp, but at 40 or more periods per 
second both work well. The pulsating current is also applicable 
to the charging of storage batteries and to other electrochemical 
purposes ; but for the operation of the ordinary direct current 
motors it would be likely to cause sparking unless the pulsations 
were “smoothed out” by inductance, storage batteries, or other 
suitable means. 

Rectifiers have been more generally employed in England than 
in America, the Ferranti type being used in a number of stations. 
This consists essentially of a synchronous alternating current 


918 ELECT RICAIIOCHTING 


motor driving the rectifying commutator. A constant current 
transformer with movable coils somewhat similar to that shown in 
Fig. 135 is employed in connection with this rectifier, which is 
usually applied to arc lighting. 

An interesting example of rectifier is that installed by Mr. W. 
S. Barstow in Brooklyn. The 6600 volt three-phase current from 
the main generating station is supplied to the primary of a con 
stant current transformer of the type illustrated in Fig. 135, the 
secondary circuit at 6600 volts is led through the rectifier, which 
consists simply of a three-part commutator driven by a synchron- 
ous motor, the three-phase conductors being connected respectively: 
to the three segments of the commutator. Two brushes set dia- 
metrically opposite each other are applied to the commutator, and 
are connected to a series circuit of arc lamps. The standard form 
of Thomson-Houston commutator is employed with the usual 
blower attachment to suppress sparking. Since the Thomson- 
Houston armature has practically a three-phase winding of the Y 
form, the current supplied to its commutator segments is practi- 
cally the same as in a three-phase rectifier. In the latter case the 
commutator is placed at a distance from the armature winding, and 
is driven by a synchronous motor. Owing to changes in the phase 
of a motor when variations in load, etc., occur on the circuit, the 
position of the brushes may not agree exactly with the points of 
zero current, so that sparking will occur. Since the maximum 
potential exists between adjacent commutator segments separated 
only by a small air-gap, there is a strong tendency to flashing or 
“ring-fire’’ around the commutator, thus short-circuiting a pres- 
sure of several thousand volts. This constitutes the chief difficulty 
in the operation of rectifiers. 

The direct current obtained by rectifying a two- or three-phase 
current does not pulsate so much as the rectified single-phase cur- 
rent in Fig. 175, for the reason that in the former-case two or 
three waves are superimposed. If, for example, we reverse all the 
waves below the zero line in Figs. 110 and 114, the resulting 

direct current would be represented by a curve obtained by sum- 
| ming up the ordinates at every point, the fluctuations being much 
/ less than in Fig. 175. 
beer eee Changers. — As their name implies, these machines 
are used for changing the frequency of an alternating current. 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 219 


Ordinarily the object is to increase a low frequency of say 25 
periods per second, which is hardly high enough for arc or incan- 
descent lighting, to 60 periods for example, which is more satisfac- 
tory for the purpose and is also suited to the usual types of motors 
and transformers. The type of frequency changer made by the 
General Electric Company is essentially a polyphase transformer 
with a movable secondary. The latter consists of a secondary or 
armature suitably wound for any desired voltage and phase, which 
is mechanically revolved and acted upon by the rotating field of a 
polyphase primary. If the secondary is revolved in a direction 
opposite to that of the rotary field, obviously the frequency of the 
current in the secondary will be higher than the frequency of 
the current supplied to the primary, and vice versa. When the 
secondary rotates against the rotary field, it acts as a generator 
and requires power to drive it, and when it turns with the field the 
machine acts as an induction motor. Thus we see that there is a 
combined generator and transformer action when the frequency is 
raised. 

The secondary may be rotated by any suitable mechanical 
means, the synchronous polyphase motor being ordinarily used 
for this purpose. By over-exciting the field of the latter, the lead- 
ing current thus produced (p. 134) may be made to balance the lag 
caused by the primary of the frequency changer, thereby raising 
the power factor on the supply circuit. The output of a frequency 
changer when the frequency is increased is equal to the sum of 
the mechanical power applied to it and of the electrical imput in 
the primary, less the losses. The frequency of the secondary 
current is equal to the number of poles of the primary, multiplied 
by the sum of the revolutions per second of the shaft and of the 
field (when they run in opposite directions). Ifthe primary has a 
three-phase winding and the secondary is provided with a two- 
phase winding, the current is changed from three- to two-phase at 
the same time that the frequency is raised. It is evident also that 
the opposite change may be effected by transposing the windings. 

Tests of a 200 k.w. General Electric frequency changer of 
this type gave the following results : 


Primary wound for 6000 volts, 3 phase and 25 cycles. 
Secondary “ 5S DAVOS im 2 tae 6 ‘ae G24 aNce 


220 ELECTRICOLIGH TING. 


The above machine was directly connected to a 4-pole, 3-phase, 
6000-volt, 25-cycle (hence 750 7f.m) synchronous motor with a 
stationary armature. ‘The efficiency was 73} per cent at 80 k.w. 
output, 814 at 120 k.w., 874 per cent at 160 k.w., and 91 per 
cent at 200 k.w. or full load. The power factor was practically 
100 per cent at all these loads, showing the balancing of the lag- 
ging and leading currents as already pointed out. The wave forms 
of £.4/./. and current approximated closely to the simple sine 
curve. ‘The efficiencies stated above signify the true watt output 
divided by the true watt imput, the latter including the true watts 
consumed by the motor. 

Transforming from Two- to Three-Phase. — It has just been 
explained how the frequency changes may be employed to trans- 
form currents from two- to three-phase, or wvece versa. This 
requires, however, two rather expensive machines demanding at- 
tention, so that when no change in frequency is desired, it is more 
economical to transform from two- to three-phase, or the converse, 
by means of simple static transformers. A method of this kind, 
devised by Mr. C. F. Scott,* ‘is llustrated in Figs. 176-178. It 





Figs. 176 and 177. Transforming from Two- to Three-phase. 


involves the use of two transformers, one wound for a ratio of 
transformation of say 1000: 100, and the other for a ratio of 
1000: 86.7. In, Fig. 176, H/ ‘represents the primary:and AB 
the secondary of the first transformer, A/V and C/ being respect- 
ively the primary and secondary of the second transformer. The 
two primaries are fed from the two-phase circuit D/ and /G, and 
one terminal of the secondary C/ is connected to the middle: point 
of the secondary AZ. The three-phrase circuit is connected to 
the points AB and C. In the diagram of potentials (Fig. 177) it 
is evident that AC and CB will each be equal to AS, so that ABC 


* Electric World, March 17 and 24, 1894. 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 221 


will be an equilateral triangle when C7: AB:: V3:2::86.7: 100,. 
hence the three secondary £.J/./’s. represented by AA’, LC and 
CA, are equal in value and differ by 120° in phase. This is the 
proper condition for supplying a three-phase circuit connected to 
the points A, B and C. In practice, especially in small trans- 
formers, it is a sufficiently close approximation if the A.JZ./. of 
the secondary C/ is 90 instead of 86.7 per cent of AB. 

This method is often employed when two-phase energy is pro- 
duced by the generators (see Fig. 178) and it is desired to trans- 
mit some or all of it to a considerable distance. By transforma- 
tion from two- to three-phase, a saving of twenty-five per cent in 
copper is secured in the Lranemittines conguctors:A A.C. At the 
receiving station the energy may be distributed in three-phase 
form or may be transformed back again into two-phase current as 
indicated in Fig. 178. The large generators at Niagara are of the 





Fig. 178. Phase Transformation. 


two-phase type, and some of the energy produced by them is trans- 
formed in the above-described manner, so that it may be trans- 
mitted in three-phase form. — 

Transforming from Single to Polyphase.— It is often very Wenge: 
able to accomplish this result when it is required to operate motors 
from single-phase circuits, but the subject belongs to electric power 
more than to electric lighting. A method of this sort, invented by 
Mr. C. S. Bradley,* consists in causing, by means of a condenser, 
a lead of current in one branch of a circuit, and in combining this 
with lagging currents in another branch so as to produce a three- 
phase current in the secondary circuit. 

Size and Location of Transformers.— Most systems of alternat- 
ing current distribution employ transformers, and it is of great 
importance to exercise special care in deciding upon their sizes and 
locations. The constant core loss results in the course of a year 


* Phasing Transformers 7rans. Amer. Inst. Elec. Eng., September, 1895. 


IAA ELECTRIC LIGHTING: 


-in a waste of a large amount of energy, and every effort should be 
made to reduce this to a minimum. When transformers were first 
introduced, it was customary to use a large number, of them in 
small sizes; but it was soon found that the core loss consumed 
too great a fraction of the total output of the station, often amount- 
ing to 25 and sometimes to 50 per cent. This was partly owing 
to the fact that transformers at that time were not as well designed 
and constructed as at present, but it was due also to the custom of 
using too many small sizes. This is made evident by inspecting 
the table on page 184, which shows that a 600 watt, 125-cycle 
transformer has a core loss of 20 watts, while one of 50,000 watt 








ne 
8) 
= 
Le: 
ce 
5 
= 


Second Ave. 





Fig. 179. Number and Arrangement of Transformer. 


capacity, or 83.3 times as great, has a core loss of 354 watts, 
which is only 17.7 times as much. In the first case the loss’ is 3.3 
per cent, and in the second it is but .7 per cent, or about one-fifth 
as large. If the comparison be made between the 1 k.w. and the 
10 k.w. transformers, it is found that the former has a core loss of 
2.5 per cent (25 watts) and the latter of 1.08 per cent ; these being 
the limits of sizes ordinarily used in electric lighting. 

The actual case of a district in a small town is represented in 
Fig. 179. Originally there were installed 25 small transformers 
(indicated by dots and numbers) having a combined capacity of 340 
lamps of 16 c.p. and a core loss of 1664 watts. These were after- 


ALTERNATING CURRENT SYSTEMS OF DISTRIBUTION. 223 


wards replaced by two larger transformers (indicated by black 
rectangles), which had only 238 watts core loss, or about one- 
seventh as much, the saving being 1426 watts. If the first plant 
operated for 24 hours per day the core loss would have aggregated 
40 k.w. hours for each day in the year, and probably this was 
greater than the useful energy consumed in the lamps. This may 
be a rather extreme case ; but there were many others equally bad, 
and at one time the average practice was little better.” Besides the 
advantage of lower percentage of losses in large transformers, a 
gain is made in the fact that the total required capacity is less. 
If, for example, a small transformer is installed for each house, it 
is necessary that its size should be sufficient to supply the maxi- 
mum number of lights that will ever be used in that house at one 
time, ~ Ordinarily, in fact for fully 99 percent of thésyear, the 
number of lamps burning will be much less than this maximum, 
hence the transformer and its core loss are far out of proportion to 
the average useful current. On the other hand, a larger trans- 
former, supplying ten houses for example, need not have ten times 
the capacity, because it is practically impossible that all of the 
houses will burn the maximum number of lights at the same time. 
In short, one 7.5 k.w. transformer will safely take the place of 
ten transformers of 1 k.w. each ; and the former would have a core 
loss of only 85 watts compared with 10 x 25 = 250 watts for the 
latter. 7 

A further saving may be effected by having sub-stations in 
which the transformers are concentrated or “ banked,” and con- 
nected in parallel. During the hours when the load is light, only 
one transformer need be operated, the primary circuits of all the 
others being open; but when the load increases transformers are 
added as required, thus the core loss is kept in reasonable propor- 
tion to the useful energy. 


224 ELECTRIC LICLLING: 


- 


CELA PET: 
CALCULATION OF ALTERNATING CURRENT CIRCUITS. 


THE properties of' electrical conductors were given in Chapter 
I., which included a general discussion of economy in their design. 
The principles there laid down apply to alternating as well as to- 
direct current conductors, but additional factors enter in connec- 
tion with the former. In the long-distance transmission of power, 
these questions are of prime consequence; but in electric lighting 
the distances are ordinarily shorter, so that the problem is not so 
difficult or important. Hence it will not be necessary to consider 
the matter in detail or at great length in this work. 

Choice of Frequency. — One of the first points to be decided in 
designing an alternating current system is the best frequency to 
employ. Those generally used in the United States are 25, 40, 
60, 125, and 133 cycles per second. It would be well if the 
Standardization Report of the American Institute of Electrical 
Engineers were followed and three standard frequencies of 30, 
60, and 120 became generally adopted. These would cover almost 
all cases that arise, and being simple multiples of each other would 
facilitate the design and construction of apparatus in regard to 
number of poles, windings, etc. In other countries many different 
frequencies are employed, 100 cycles being a common value in 
Ingland and on the Continent. Sixty cycles or less is considered 
to be “low frequency,” and above that is called “high frequency,” 
but anything between 60 and 120 is rarely used in America. A 
frequency of 135 cycles was originally adopted when the alternat- 
ing current was introduced for electric lighting, and is still used in 
many plants, especially those installed by the Westinghouse Com- 
pany. A standard of 125 cycles is adopted for electric lighting 
apparatus by the General Electric Company. These high frequen- 
cies possess the advantage that the size and cost of transformers are 
less when they are selected. At the present time a 10 k.w. trans- 


CALCULATION OF ALTERNATING CURRENT CIRCUITS. 225 


former costs about 25 per cent more for 60 cycles and about 60 
per cent more for 25 cycles than for the high frequency of 125 
cycles. | 

In the early history of alternating current lighting, the gene- 
rators were belt-driven and ran at about 1000 r.p.m. Consequently 
133 cycles could be obtained with a 16-pole machine. At present 
large direct-connected alternators running at about 100 r.p.m. are 
generally installed, and would require 160 poles to give the same 
frequency. This would make a complicated and expensive con- 
struction, so that 60 cycles, requiring 72 poles, would be much more 
practical. Another objection to high frequency is the fact that 
inductance or capacity effects are greater. The drop in voltage 
due to the former and the charging current due to the latter are 
both directly proportional to the frequency, and the tangent of the 
angle of lag is also proportional to it. For example, the voltage 
drop on a No. 0 A.W.G. wire due to its resistance and reactance 
(p. 116) is only one-half as much at 265 as it is at 125 cycles. 
Tables showing this difference will be given later in the present 
chapter. Since the drop is greater it follows that the regulation 
is poorer on high frequency circuits. The greater wattless cur- 
rents cause greater heating in generators, lines, transformers, etc. 
Still another disadvantage of high frequency is the fact that it 
renders more difficult the parallel operation of generators and 
rotary converters, as well as the running of motors. 

The disadvantages of low frequency, besides the higher cost of 
transformers already noted, are the difficulties involved in operat- 
ing arc and incandescent lamps. It is not yet practicable to run 
the former below 40 cycles and the latter below 25 cycles per second, 
and even at those values the results are not very satisfactory. 
Low-voltage or large candle-power incandescent lamps flicker less 
than the standard 110 volt 16 c.p. lamps, but the practice is deter- 
mined by the latter. The 220 volt lamp would be still more sen- 
‘sitive to the waves of current, on account of its thinner filament. 

In conclusion, it may be said that for lighting alone at moder- 
ate distances a frequency of 125 or 133 may be adopted ; but even 
in such cases it would probably be wiser to choose 60 cycles, in 
order to permit the operation of motors and the extension of the 
system to greater distances. For supplying power as well as light 
60 cycles are very satisfactory where the circuits are not too long. 


226 ELECTRIC LIGHTING, 


To transmit energy to great distances, a low frequency, such as 
25 or 80 cycles, is suitable. The same is true of long underground 
or submarine cables where the capacity effects would be great. A 
low frequency of 20 is generally selected also for the simple trans- 
mission of energy between generating and distributing stations, 
where the energy is converted into direct current before it is used, 
so that the frequency makes no difference so far as the lights are 
concerned. This question, which is almost always a serious one, is 
often complicated by the fact that a certain frequency has already 
been adopted in the original plant, so that there is a great tempta- 
tion to adhere to it in making additions. In many cases it may be 
necessary to do so; but frequently it would be wiser and cheaper in 
the end if the old-fashioned apparatus were sold, even at a great 
sacrifice, and a new plant designed and installed in accordance with 
the best practice. 

Relative Weights of Copper for Various Systems. — This 
question is exceedingly important, but belongs more to long-dis- 
tance power transmission than to electric lighting. Nevertheless, 
the problem often enters directly or indirectly in electric light 
engineering, and it will be well to consider briefly the principles 
involved, and the methods of calculation that are employed. 

A comparison between the weights of copper required for the 
different direct-current systems was given on page 87. In at- 
tempting to apply similar reasoning to the alternating current, the 
difficulty arises that the voltage ordinarily measured is not the max- 
zmum value; and since the insulation is subjected to the strain of 
the latter, the relative figures obtained depend upon which basis of 
comparison is adopted. For long-distance transmission the highest 
voltage that is practicable under the circumstances would ordinarily 
be chosen, but for local distribution the effective pressure would 
determine the question. 

The most important systems of transmission and distribution 
are represented in Fig. 180, and the relative weights of copper 
required are given in terms of the common two-wire circuit taken 
as 100. For equal effectzve values of £./.F. the direct and alter- 
nating currents demand the same weight of copper; but if equal 
maximum values are considered, the latter requires twice as much 
copper, distances, power in watts, percentage of drop, etc., being 
equivalent. This is easily understood when we remember that the 


CALCULATION OF ALTERNATING CURRENT CIRCUITS, 227 


maximum value of an alternating Z.I.F. is V2 = 1.41 times its 
effective rating, consequently an alternating 4.1/7.7. of 100 volts 
would have the same maximum as a direct £.M.F. of 141 volts. 


System. Connections. Weight 
of Copper. 

Single Phase 

75 Wire : 100. 
Single Fhase 375 

3 Wire 15 0.0 

Two Phase 

3 Wire Lente 
Two Phase 

3 Wire (1457 
Three Phase ; 

Wire TEE 


_ Three Phase 
4 Wire O55 


Monocyclic { 28 
150. 


Fig. 180. Relative Weights of Copper. 





For the same number of watts the amperes of the direct current 


are as great, so that the drop in volts is in the same propor- 


00 
141 
tion with equal resistances. But the percentage of drop is only 
LOORen LOOM 


= —as large for the current, or one-half as much copper 


aL Oakey ee 





228 | ELECTRIC LIGHTING. 


would be required for the same percentage of drop. This is sim- 
ply a particular case under the general law that wezght of copper 
zs inversely proportional to the squares of the voltages, other things 
being equal. 

The single-phase, three-wire (Fig. 150) requires 374 per cent 
as much copper as the two-wire system, and by making the neutral 
one-half the cross-section of either of the outside conductors the 
copper is reduced to 314 per cent. These percentages are in the 
same proportion as for direct-current systems, the figures for which 
were explained on pages 72 and 87. The above ratios assume 
that the lamp voltages are equal in all cases ; but it is evident that 
this will give twice the zofa/ voltage for the three-wire circuit, since 
it practically involves the placing of two lamps in series. For the 
same ¢ofa/ voltage, the three-wire would require 50 per cent more 
copper than the two-wire system, since the former would have 
three conductors instead of two, and everything else would be the 
same. 

Two-phase four-wire require the same amount of copper as the 
ordinary single-phase two-wire circuits, the former being equivalent 
to two single-phase systems. With the two-phase three-wire sys- 
tem (p. 142) the case is not so simple, but may be determined as 
follows: Assume the voltage V between either outside wire and 
the common return wire to be the same as ina single-phase cir- 
cuit. The total power transmitted is V/ for the latter, where / 
is the current, and to transmit the same power by the two-phase 
system the power must be 2 lz, in which z is the current in either 
outside wire, and is equal to 7+ 2. The current in the common 
conductor is z v2. consequently to have the same current density, 
which is the condition of maximum efficiency, its cross-section 
must be V2 times that of either of the others, and its resistance 
is *-+ V2 in which r is the ohmic resistance of one of the outer 
wires. The loss of power for each of the latter is 277, and for the 
middle wire it is 2 727+ V2 = 7%, V2, hence the total loss in the 
three wires is 2227 + 72rV2 = 7% (2+ V2) =/7 (24+ V2)+ 4, 
since 7= 7+ 2. The loss in the equivalent single-phase circuit is 
27?R, in which R is the resistance of one of the conductors, and 
this must be the same as the loss for the two-phase system ; hence 
[27 (2 a2 


) 2 = =. V2) re oe a epee Eee 
id lial 4 or 7 a4 ai; 


CALCULATION OF ALTERNATING CURRENT CIRCUITS. 229 


Therefore each outer wire must be (2+ V2) +8 times, and the 
middle wire V2 (2+ V/2) + 8 times as large as each single-phase 
conductor. It follows that the wezght of copper in the two-phase, 
three-wire conductors 1s re) " 2 ae (Ces UC ue) 2 = 1.457 com- 
pared with 2 for the singlephase, two-wire system, or tn other 
words 1s 12.9 per cent as great at the same minimum voltage. If 
this comparison is made on the basis of maximum voltage, it is 
necessary to make the potential difference between the outer con- 
ductors equal to that in the single-phase, two-wire circuit, hence 
the voltage between either outside wire and the common return is 
V + “V2, and the current in each branch z, = / + v2; so that the 
power in both branches is 2(V+ V2)(7+ V2) = VJ, which is 
the same as that in the single-phase system. The current in the 
common return is 7, V2 = /, and its resistance should be 4 + V2 
if 7, is the resistance of each outer wire. The total loss is 





. 29 b. ee 


This must be equal to 2/2, the loss in the single-phase, hence 


2 2 4k 
17, (2+ V2) — May ae. or V5) — ere ee ares a © 
2 PE A) 
. ee aN Ose 
That is, each outside wire requires ae times, and the 


middle wire times as much copper as each of the 


(2+ V2) V3 
4 
single-phase conductors. 
Hence the total system demands 
Di Dee Dye (2 bea DAD 
ta 
gle-phase, or 1.457 times as much copper; that is, the two-phase 
three-wire system requires 45.1 per cent more copper than the two- 


= 2.914 compared with 2 for the sin- 





phase at the same maximum voltage. 

Considering a three-phase, three-wire system (p. 145), having a 
voltage VY between the lines measured as A potential, the current 
in each line, or Y current, is 7, and the current from line to line, 
or A current, is 2, V3. Hence the total power in all three 
branches is 3/7,-+ V3 = 17, V3, and if this is to equal V/, the 
power of the single-phase circuit, then V7 = Vz, V3, or 7, =7+ “V3. 


230 ELECTRIOULIGAHLING 


If ~ is the resistance of each three-phase conductor, then the loss 
per wire is /77, + 38, and the total loss is /*7,, while in the single- 
phase system it is 272. Hence, to get the same loss, /47, = 2/2R, 
or ry = 2R; that is, each three-phase wire has twice the resistance 
and half the copper of each single-phase conductor, or in other 
words, the three-phase, three-wire system requires TS per cent as 
much copper as the single-phase at the same maximum voltage. In 
the three-phase, three-wire system, with the lamps connected be- 
tween the neutral point and the three outer wires, — that is, in Y 
fashion (p. 144),— the voltage between the outer wires, or A poten- 
tial, will be / V3, if Vis the lamp or Y voltage. In other words, 
the potential between lines is raised from V to VV8; and since it 
has been shown previously that the weight of copper is inversely 
as the square of the voltage, the weight of copper for the three 
wires will be one-third as great as in the preceding case, and3 + 3 
= 4as much as for the two-phase. The addition of a fourth or 
neutral conductor (Fig. 166) will increase this to 4 x 4 = 3, so 
that the three-phase, four-wire requires 33.5 per cent as much copper 
as the single-phase, two-wtire system at the same minimum voltage. 

The monocyclic system, when supplying lamps, is practically 
the same as a single-phase circuit (p. 208); and most of the energy 
for motors is carried by the two main conductors, except in starting, 
when the auxiliary wire furnishes a certain amount of current. If 
the extra wire is omitted on certain circuits, then the copper re- 
quired is the same as for the single-phase, two-wire system. If the 
third wire is one-half as large as each of the other two, then the 
monocyclic calls for 125 per cent ; and if the three conductors are 
all of the same size, then the copper demanded is 150 per cent of 
that used by the single-phase circuit. Hence the monocyclic system 
requires as much copper as an equal voltage single-phase, two-wire 
system, plus the copper in the auxiliary conductor. 

This table is issued by the General Electric Company, and gives 
in convenient form the constants to be used in calculating over- 
head electric transmission lines, the various quantities having the . 
following significance : — 


x = Ohmic resistance. 

LZ = Inductance in milhenrys per 1000 feet of conductor. 

C= Capacity in microfarads per 1000 feet of conductor. 

7, = Charging current at 100 cycles and 10,000 volts to neutral, that is, ina 
20,000 volt single-phase, and a 17,300 volt three-phase line. 


CALCULATIONS OFMALTERNATING CURRENT CIRCUITS.” 231 


to= 2 X mw X frequency X CX E X 10 —*; where Z is the Z.AZF. between a 
line and neutral. : 

x = reactance = 2 X m X frequency X Z X 10—%, 

The £.4Z.F. consumed by resistance 7, of the line, is = /y, and in phase with the 
current /. 

The £.4Z/. consumed by the reactance x, of the line, is = 7x, and in quadrature 
with the current 7. 

The £.47./. consumed in the line is neither /r nor /x, but depends upon the 
phase relation of current in the receiving circuit. 

The loss of energy in the line is= 727, hence does not depend upon the reac- 
tance, but only upon the resistance. 

Two wires in parallel have the same resistance and about half the reactance (if 
strung on separate insulators and intermixed) of a single wire of double cross-section. 
Thus replacing one No. 0000 wire by two No. 0 wires, the resistance, weight of cop- 
per, etc., will remain the same, but the reactance will be reduced practically to half, so 
where lower reactance is desired, the use of several conductors, strung on indepen- 
dent insulators and intermixed, is advisable. 

The values given for Z, C, 2, and x are calculated for sine waves of current and 
EMF. 


LINE CONSTANTS FOR ELECTRIC TRANSMISSION. 
Per 1000 Feet of Eacu WIRE. 


REACTANCE AT 


25, 60, 125 CycuEs, 


(toe? is 
MILHENRYS. 
CAPACITY IN 
MICROFARADS, 
RENT. 


IN OHMs. 


S1zE oF WIRE 
A.W.G., 
WEIGHT 

DIAMETER 
RESISTANCE AT 
INDUCTANCE IN 
CHARGING CuR- 





C.M. 





211600 | . : .00388 
167805 | . : .00578 


133079 | . P .00368 
105592 | . : .00358 


5694 | . ‘ .00351 
66373 | . : .00342 
52633 | . : .00334 
41742 |. ‘ .00326 
38102 | . : .00320 
26250 | . : .00315 
20816 | . ‘ .00306 
16509 | . : .00300 
13094 | . : .00294 
10382 | . as) .00288 


























OD ON OO RW NH 


rea 























The above figures apply to parallel wires that are 18 inches 
apart, but are not much modified by moderate changes in interaxial 
distance. For example, the inductance Z is decreased about 10 


232 ELECTRIC LIGHTING. 

per cent when the wires are 12 inches apart; and is increased about 
10 per cent when they are put 30 inches apart. A similar change 
would be produced in the reactance 2rfL. The capacity C and 
charging current z, are increased about 10 per cent, if the inter- 
axial distance is reduced to 12 inches; and is decreased about 10 
per cent when it is raised to 80 inches. or wires placed close 
together in cables, the inductance and reactance would be greatly 
reduced, and the capacity and charging current greatly augmented, 
so that their values in the table would not be even approximately 
true. In such cases, or whenever there may be any doubt, the 
general formule for inductance and capacity, given on pages 129 
and 187 respectively, should be used. The table on page 150 
shows the inductance of wires from No. .0000 to No. 12, and for 
interaxial distances from 3 to 96 inches. 

The equations on page 138 give results for capacity that are 
twice as great as those found in the above table, the reason being 
that each conductor is considered separately with respect to zevo 
potential, which would ordinarily exist at a point midway between 
two wires forming a circuit ; whereas the equations (p. 158) give 
the capacity with respect to the other were, which is one-half as 
much. Thecalculated charging current would be the same in both 
cases, because the total voltage would be used in one instance, and 
the potential with respect to zero is taken in the table. The latter 
plan is generally better. Other convenient tables issued by the 
General Electric Company are given below. They apply particu- 
larly to overhead circuits with wires 18 inches apart, and are suffi- 
ciently accurate for most practical purposes, when the distance 
between wires is approximately that amount. If the conductors 
are less than 18 inches apart, the loss in voltage is lower than that 
given by the formule, and if they are close together, as in cables 
or interior wiring, the loss will be only that due to resistance. 

The following general formulz may be used to determine the 
size of copper conductors, current per conductor, volts loss in lines, 
and weight of copper per circuit for various systems of electrical 
distribution. 





! DD SGV LG 
Area of conductor, Circular Mils = Piers (77) 
Wax: 
Current in ‘main conductors = —_-- (78) 


ie 


CALCULATION OF ALTERNATING CURRENT CIRCUITS: -233 


PERL, 
Volts loss in lines = 100 ; GEG) 


TD ye NES I em ere | 
P x E? x 1,000,000 








Lbs. copper = (80) 
W = Total watts delivered. 
D = Distance of transmission (one way) in feet. 
P = Loss in line in per-cent of power delivered, that is of W. 
£ = Voltage between main conductors at receiving or consumer’s 
end of circuit. 
Homcontinuousrcurrent 7 = 2100 710 17 = 1 and A = 6.04. 


CONSTANTS FOR ELECTRICAL CIRCUITS. 


VALUES OF K. VALUES OF T. 





SYSTEM. Per Cent Power Factor. [ Per CeEnT Power FAcror. 





VALUES OF A. 


100 95 80 








Single-phase . . 2160 | 2400 | 3000 
Two-phase (4-wire) 1080 | 1200 | 1500 
Three-phase (3-wire) 1080 | 1200 | 1500 


Soe ES 
oo > 
SOR 






































VALUES OF M. 





25 CYCLES. 60 CYCLEs. 125) Cy CLES, 





Per Centr Power PER CENT POWER Per Cent PowsER 
FACTOR. FAcTOR. FACTOR. 





i 
2 
= 
fh 
° 
zi 


A. W. GAUGE. 
No. oF WIRE. 


A. W. GAUGE. 


ee) 
—) 
~ 
i) 
ea) 
—) 


90 | 85 90 





| 


“13 
es) 
Ore 
CO 
S 
> 
S 
SS 


bo co 
“ICO rR AbD 


CO ON 
Coo wo NHK 


pt et 
ho bo 
=o wo 











Oo eH He CO 
an Bo 


am —_} ef 
Ino Oc 
bo on 

S 
sic 


oO 


(ate gpa fain, pear ery See eee 
no eo 


et a ee et et ee me bo bo bo 


na 
SO Od CO Od 





OID ON GMO WG 


He CO be 


bo co 
SB 





be 
Co co LY: 
oS So -oo (ome cs 


ES SS Syog 
Hr bow Bo 
bb wb Oa 


oe “IO 























© bv = OO oA Wo OW Oe 
aa co cet ce ec ed we cll wc 


25 CSO ODO tO HE 

SS 65 Sh Ea 

WS Cl CO COO HH bw 

BO CS 565 BOK OD BSH 
G25 OS CO HH pw BRO 

ie eee nee 
SOD Ou tw Re 


of O- 








> 
oO 
etl tn cell eet cel oe cl cee eo 


CO SSO COO HH Nw Ba Do 
SS SS OWS HHO oR GO AS 


Some con oC Ome hoo ec 
ye tls mes ie ie RS i TS) 


Lc ae eee ee ee cl oe cc eld 
a a et bo bo bo 0 


SOD OH NW BOA NO 
ob Ao Fe wa aA 





Sore o> 
SOW) So 
Sooo 

Ro 16:5 3Se 

Sie Os oe co 
SCO WI On 


= 
oODoD ON Oo HCO 
SS 

(==) (==) 

Qs) SS 

Si=) 

oo. h6hcOrF 

H= OD © bo 

W Od 

jot jt 

_—_ 


> 
Oo 





234 ELECTRIC UIGHTING. 


The value of A for any particular power factor is obtained by 
dividing 2160, the value for continuous current, by the square of 
that power factor for single-phase, and by twice the square of that 
power factor for three-wire, three-phase, or four-wire, two-phase. 

The value of 17 depends on the size of wire, frequency, and 
power factor. It is equal to 1 for continuous current, and for 
alternating current with 100 per cent power factor and sizes of 
wire given in the preceding table of wiring constants. 

The value of Z depends upon the system and power factor. It 
is equal to 1 for direct current and for single-phase current of 100 
per cent power factor. 

The value of A and the weights of wire in the table are based 
upon .00000502 lb. as the weight of one mil foot of copper. 

It should be observed that P stands for the per cent loss of the 
delivered power, and not the per cent loss of the power at the gen- 
erator; and that £& is the potential at the end of the line, and not 
at the generator. ¢ 

When the power factor cannot be more accurately determined, 
it may be assumed to be as follows for any alternating current sys- 
tem operating under average conditions: Lighting with no motors, 
95 per cent; lighting and motors together, 85 per cent ; motors 
alone, 80 per cent. The size of wire in (77) is for each of the main 
or outside conductors of a given system, for example, the three 
wires of a three-phase, the four wires of a two-phase, or the main 
two wires of a monocyclic system. The neutral wire in the three- 
wire system for direct (p. 72) or alternating currents (p. 192) may 
in the case of feeders be made one-half or one-third size, or omitted 
entirely (p. 76), depending upon how well the system may be bal- 
anced. For local or secondary circuits it should generally be the 
same size as each of the main wires. These statements also apply 
to the middle wire of the four-wire, three-phase arrangement (Fig. 
166). The size of the auxiliary conductor in the monocyclic sys- 
tem should be in the same proportion to either main wire as the 
motor load in amperes is to the total load in amperes. 

A simple method of calculating the drop and other data of 
alternating current circuits is represented in Fig. 181, being 
derived from the little book on Alternating Current Wiring and 
Distribution, by W. L. R. Emmet. Assume a case where 500 
incandescent lamps, of 57.5 watts each, are to be fed from the sec- 


CALCULATION OF ALTERNATING CURRENT CIRCUITS, 235 


ondaries of transformers of different sizes, being half loaded on the 
average. The primaries are supplied by two No. 2 wires from the 
generator two miles distant, the wires being 18 inches apart, and 
the frequency of 125 periods per second. The voltage of the 
lamps is 100, and the ratio of transformation is 10. In Fig. 181 
the horizontal lines represent energy components, and the vertical 
lines inductive components of £.4/./. For the sake of uniformity 
the lamp voltage is multiplied by 10, the ratio of transformation 
making 1000 volts, which is represented by the horizontal line AB, 
since incandescent lamps are practically non-inductive. Assuming 
the secondary wiring to have an energy loss of 3 per cent, BC is 
laid off as 30 volts, and an inductance component CD, of the same 
amount. (Both of these are rather high values.) Take the resist- 
ance in the transformers at 1 per cent, and the inductance loss at 





Fig. 181. Graphical Calculation of Alternating Current Circuit. 


one-half load as 12.5 per cent of AD, or about 13 per cent. Hence 
we lay off DF = 10 volts to represent resistance, and FG = 130 
volts to represent inductive loss in the transformers. If there were 
no losses in the transformers, the current received by them would 
be 28.75 amperes, but with 5 per cent iron loss at half-load this 
becomes 30:19 amperes. The resistance cf four miles of No. 2 
wire from the table on page 8 is .156 x 5.28 x 4 = 3.3 ohms, 
and the reactance at 125 cycles is .249 x 5.28 x 4 = 5.25 ohms. 
To this we add 15 per cent for distortion of current waves, making 
6.04 ohms. The resistance drop is 30.19 x .83 = 99 volts, and 
the reactance drop is 30.19 x 6.04 = 1.82 volts, which are laid off 
as GHand HK. Hence the line AK represents the EMF. re- 
quired at the generator terminals, being 1188 volts. Extending 
Kf to /, we have A/ the total energy component of 1139 volts, 
therefore the real power in the circuit is 11.39 x 30.19 = 34,300 


236 ELECTRIC LIGHTING. 


watts, while the volt-amperes at the generator are 35,800, so that 
an alternator of 36 k.w. capacity will be required ; but the power to 
drive it, assuming its efficiency at 90 per cent, will be 34.3 + 
.90 = 88 k.w., or 51 h.p. The generator should be overcom- 
pounded about 19 per cent to be self-regulating. 

Arithmetical Determination. — The same result that has been 
obtained graphically may be found arithmetically, as follows : 





ENERGY INDUCTANCE CURRENT IN 
COMPONENT COMPONENT AMPERES. 











IN VOLTs. IN VOLTS. 
Lamps brought to basis of 1000 volts . . . 1000 28.75 
Secondary wiring with 8 per cent resistance 
and 3 percent inductanceloss . . : . . 30 30 
1030 30 
Transformer resistance loss of 1 per cent. . 10 
5s inductance loss of 12.6 per cent 
of volts at secondary terminals. . . . 130 
Primary current increased 6 per cent by core 
loss at. balt-load gas @ (0 ihe =.) #na eee 1.44 
Line Current os 0 in © che Ls ae or ten 30.19 
Line resistance loss 3.5°X 3019.3 7) 3. G.0,. 99 
«< Inductance-loss 6.04 x S0;199) . 7. a 182 
1139 042 


Taking the square root of the sum of the squares of 1139 and 
342, we find 1188 volts to be the £.1/-F. pressure at the generator 
terminals, being the same as obtained by measurement in Fig. 181. 


OVERHEAD CONDUCTORS. . 237 


GelreASB lb Rex hI: 
OVERHEAD CONDUCTORS. 


THE term overhead conductors is applied to aerial electrical 
wires or cables carried on poles or upon brackets or other supports 
attached to buildings. The same general construction is used for 
telegraph and telephone, as well as for electric light and power 
lines ; but the parts are usually heavier, and the insulation higher, 
Hmet eecasced! teu woe lattcr,specause ot) thes larver size of the 
conductors and the more powerful character of the currents. 

Materials for Overhead Conductors.— For electric light and 
power purposes copper is generally employed, and has now largely 
supplanted iron wire even for telegraph and telephone lines. The 
fact that hard-drawn copper has a tensile strength of 60,000 to 
70,000 lbs. per square inch, compared with 25,000 to 35,000 for 
soft or annealed copper, makes it especially suitable for overhead 
construction. On the other hand, the specific resistance of hard 
copper is from 2 to 4 per cent greater, and it is much more brittle, 
so that it is not used for underground conductors or interior wiring 
where its greater tensile strength is not of much advantage. The 
fact that it is far less flexible makes it awkward to handle; conse- 
quently, hard copper is not convenient even for overhead con- 
ductors when they are of large size, or are covered with insulation. 
The resistances, weights, and other data of copper wires are given 
on pages 8 and 15, and in Chapter XI. 

Aluminum has a specific resistance about .6 that of copper, 
both being of pure commercial quality, therefore the sectional area 
of equivalent conductors would be about 1.67 times and the 
diameter 1.3 times greater for aluminum. The specific gravity 
of aluminum is about 2.7, and of copper 8.89 (page 8), so that an 
equal volume of the latter weighs 3.3 times as much. A copper 
wire would be (3.3 + 1.67 = 2) about twice as heavy as an alumi- 
num wire of the same length and resistance. This is a great 


238 ELECTRIC LIGHTING. 


advantage for overhead conductors, since it reduces the weight on 
poles, cross-arms, insulators, etc., by one-half. 

The tensile strength of aluminum wires is about 20,000 to 
30,000 lbs. per square inch; but the addition of a small percentage 
of copper increases this considerably, and alloyed with 24 per cent 
of copper it becomes nearly 40,000 lbs. per square inch. On the 
other hand, the resistance is increased about 20 per cent, so that 
the advantage is doubtful. Furthermore, it has been found in 
practice that wires.made of these alloys are likely to break, even 
when the tests of a sample show an ample tensile strength. ‘This 
is due to the difficulty of making perfect alloys of aluminum, 
because the light metal does not readily form a thorough and 
homogeneous mixture with the copper, which has a density 3.3 
times greater. The result is that flaws seem to exist at certain 
points on the wire, and a break may occur without excessive strain. 
In a case cited by Mr. P. N. Nunn * an average of one break per 
span occurred on a long transmission line composed of aluminum 
alloy. 

The following data for commercially pure aluminum wire are 


taken from the paper itself, and agree closely with those already 
given : 


Diameter of aluminum wire 92.0). 9.5 .ecvo.9 mis: 

Wtisper mile®.' 42) i. Nye issue eed ety Less 

Resistance; per mil foot.) 7. ware ee LO Onis ane Ce 
Resistance, per mile at 26° Co. a a eee E007 73 ohms: 
Conductivity compared with copper . . . 59.9% by dimension. 
Tensilestrength of wire. 5 7) .48 3) ee LO OUDs: 

No. of twists in six inches for fracture... . 17.9. 

Tensile strength per squareinch. . . . 32898. 


Comparing this with copper, it is seen that this wire is approx- 
imately the same as copper in the following sizes : — 


Size of aluminum wire = No. 1 B. & S. copper. 
9 


Resistance of 3 SINK, ue cc 


a“ id 


o 
Tensile strength“ “ =No.5 “* ‘6 
Weight of te =a INIOnO 


Therefore on the basis of the same conductivity the aluminum 
compares with copper as follows : — 


* Discussion of a paper “On the Use of Aluminum Line Wire,” by Perrine and 
Baum, Z7rans. Amer. Inst. Elec. Eng. May, 1900. 


OVERHEAD CONDUCTORS. 239 


Diameter for the same conductivity 1.27 times copper. 


Area I ‘“ 164 « & 
Tensile strength ‘“ &“ 629 « « 
Weight <“ “ ‘501 & ‘“ 


The number of twists necessary for fracture varies considerably, 
although the ductility test of wrapping six times around its own 
diameter, unwrapping and wrapping again, is well sustained. This 
irregularity in the twisting-test is generally a mark of impurity in 
wire; but we know so little as yet of the exact characteristics of 
aluminum in particular, and the twisting-test is in general so 
unreliable, that it is unsafe to base any exact statement on this one 
test, particularly as the wire after erection proved reliable. In 
carefully performing the test for tensile strength, no exact point 
could be assigned for the elastic limit, as the metal seemed to take 
a permanent set almost from the first; but at a stress of from 
14,500 lbs. to 17,000 lbs. per square inch, there is a marked increase 
in the permanent set which indicates that the safe working-load lies 
somewhere in this region. In this the characteristics of alumi- 
num do not differ materially from those of copper or other similar 
metals; and while this is a disadvantage, it is not a singularity. 

The fact that the wire will permanently elongate if seriously 
strained makes it necessary to use the utmost care in the erection 
of lines, and also the known high coefficient of expansion with tem- 
perature changes taken in conjunction with this property renders 
care in line-stringing especially important and difficult. The 
greatest care must be taken against kinking or scarring the wire; 
wherever the wire is accidentally kinked or scarred, it must be cut 
and spliced. 

One of the most serious problems in connection with the use 
of aluminum is in the choice of a proper joint. This metal is so 
highly electro-positive that it is unsafe to expose it to the elements 
in contact with any other material, as electrolytic corrosion is 
almost sure to follow such construction. Many of the failures 
which have been reported of this metal have been due to a neglect 
of this fact. Whenever this metal is soldered, or used in contact 
with any other metal, the joint should be thoroughly waterproofed 
to prevent such action. Without such protection the joints may 
be made by slipping the ends of the wire into an oval aluminum 
tube about nine inches long, which is then twisted about two and 


240 ELECTRIC LIGHTING. 

a half turns, with a pair of clamps similar to those employed in 
twisting the McIntire connector. The joint produced is practically 
equal to the original wire in both tensile strength and electrical 
conductivity. 

Tests made at the Columbia University showed the fusing 
points of pure aluminum wires suspended horizontally in the open 
air to be 180 amperes for No. 8, 185 amperes for No. 10, and 
60 amperes for No. 14 A. W.G. For aluminum alloyed with 
J per cent copper, the fusing-points were 163 amperes for No. 8, 
and 64 amperes for No, 14 wire. 

The use of aluminum as an electrical conductor may be 
summed up as follows: It is especially advantageous for bare 
overhead lines, because it weighs only one-half as much as copper 
for the same resistance and length, thus reducing to one-half the 
weight to be carried by insulators, cross-arms, and poles. Its ten- 
sile strength is about one-half as great as that of copper; but its 
specific gravity is less than one-third (.3) as much, so that it has 
an advantage in this respect also. On the other hand, its diameter 
is 1.5 times that of an equivalent copper wire, so that it exposes cor- 
respondingly greater surface to wind surface and to the accumulation 
of ice. The electrostatic capacity of an aluminum line is higher than 
for copper of the same resistance and length on account of its greater 
diameter, as is evident from the formulae on pages 137 and 188. 
But the capacity being a logarithmic function of the diameter 
would not be much augmented by increasing the latter by 80 per 
cent. For example, the diameter of No. 1 wire is 42 per cent 
greater than that of No. 4 wire; but the capacity of a circuit com- 
posed of two of the former, placed 18 inches apart, is only 74 per 
cent greater than if the latter were used. For overhead lines the 
electrostatic capacity of an aluminum conductor would not be more 
than about 5 per cent higher than that of an equivalent copper 
wire. Moreover, capacity does not play an important part except 
in very long transmission lines. 

Aluminum is also a very suitable material for bus bars or other 
conductors that do not require to be covered with insulation ; or in 
other words, dave conductors that are carried upon insulating SUup- 
ports, which applies to overhead lines as well. In such cases the 
fact that aluminum would have about 30 per cent more surface is 
an advantage in dissipating heat. 


OVERHEAD CONDUCTORS. 241 


On the other hand, if aluminum conductors are to be covered 
with insulating material, as in the case of ordinary wiring in build- 
ings, or especially with underground and submarine cables, then 
the fact that 30 per cent greater diameter and circumference are 
required is a disadvantage, since it increases the cost of insulation 
in about the same proportion. The lead covering or iron armor of. 
cables would also be correspondingly augmented in weight and 
cost, and the space occupied would be greater to the extent of 
about 67 per cent in cross-section. 

Sag and Stress in Overhead Conductors. — A wire suspended 
freely between two supports hangs in a curve called a catenary. 
The exact determination of the sag and other facts is somewhat 
difficult ; but for electrical lines in which the sag is usually small 
compared with the span, very closely approximate results may be 
obtained by assuming the 
curvesto beraaparapola, A’ A C B 
wire stretched between the 
points A & may be repre- 
sented by the parabolic curve 
AE &. (Vheshorzontal distance A C 2 is called the-span # in 
feet, the vertical distance JP is the deflection or sag of the lowest 
point in feet, Z is the actual length of the wire measured along the 
curve ; 7 is the tension in pounds in the wire at its lowest point, 
and W is the weight of the wire in pounds per foot. We have the 
following approximate relations : — 





Fig. 182. Sag of Overhead Wires. 


FH? W 
FT? W 
ae a ; (82) 
ONS 


With a given span // the tension 7 is a minimum when the 
sag D is one-third of H. In practice, the sag is made much less 
than this, being usually one to two per cent of the span, in order to 
avoid the strains and chances of making contact with other wires 
due to excessive swinging. 

Expansion and contraction by changes of temperature produce 
considerable effect upon the sag and tension of overhead wires. 


2492 ELECTRIC LIGHTING. 


- 


For this reason a greater sag should be allowed for wires laid in 
warm weather, in order to allow for the contraction in winter. 
The actual length Z, of a copper wire at a given temperature ¢ in 
centigrade degrees compared with its length at 20° C. is given by 
the following expression : — es 


L,=L, [1 + .000017 (¢ — 20)] (84) 


The sag with the increased or decreased length may be found 
by solving (88) for JY, which gives: 





/ 
D = Vas Cir) (85) 


The following table may also be used for determining the vari- 
ations in sag, due to temperature changes. The sag in inches is 
given for every 10° between 80° and 100° F., being the limits 
between which lines are likely to be laid. 


TEMPERATURE EFFECTS IN SPANS. 


e 
TEMPERATURE IN DEGREES FAHRENHEIT. 





FEET. 


SPANS IN 30° | 40° 50° 80° | 90° | 100" 








DEFLECTIONS IN INCHES. 





10 
12 
14 





i 


16 
18 
20 





1.2 
1.6 
1.9 





10 








TID goto bo 


“1b © 








Hard-drawn copper wire, 60,000 pounds strength per square inch. 
Stress at — 10° F., 30,000 pounds per square inch. 

At —10° F. the sag is reduced, by the contraction, to the very 
small values shown in the table; and the tension in the wire is 
raised to 30,000 lbs. per square inch, which is rather too near the 
breaking stress, assumed to be 60,000 Ibs. per square inch. 


OVERHEAD CONDUCTORS. Ay 


Hence it appears that the sag of about 1.7 per cent at 70° F., 
upon which the table is based, gives excessive tension if an over- 
head line, even of hard-drawn copper, is exposed to temperatures 
of —10° F. or less. 

The stretch which occurs in wires considerably modifies the 
results obtained by calculations, using the ordinary formulae. This 
is particularly true of soft-drawn copper and aluminum, which show 
some permanent elongation with any considerable tension applied 
to them, and do not seem to have a definite elastic limit, like steel. 

Poles. — In most cases wooden poles are employed to support 
overhead electrical conductors. But in some countries, notably in 
India, zvoz poles are used almost exclusively for telegraph and other 
electrical lines, because wood is rapidly destroyed by white ants. 
This is true of most other tropical regions. ‘The form of iron 
pole generally adopted is hollow and tapering, being similar in its 
general size and proportions to the natural wooden pole, but some- 
what smaller in diameter compared with length. It consists of 
sheet iron riveted together, and may be made in convenient 
lengths, the ends of which are fitted into each other. ‘These set 
into a cast-iron base or sole plate, which is buried in the ground. 
In order to protect the iron, it should be galvanized inside and out, 
and should also be treated with some resinous material inside and 
outside, as far as it is buried in the earth. The insulators are 
carried on iron brackets, which are bolted to the pole, making a 
very strong and neat construction. In this country iron poles are 
made of sections of wrought iron pipe, with the joints either 
“swaged’”’ or rusted. Sometimes for use as anchor poles, iron 
lattice construction is used. 

Iron bases or sockets are often employed with wooden poles, 
enabling the latter to be made smaller in diameter and straighter. 
This also overcomes the objection to iron poles, due to the fact 
that they offer a ground connection to the wires or to the work- 
men, which in the case of the latter is very dangerous with high 
voltages. 

‘Wooden Poles. — Chestnut is a very good material for this pur- 
pose, especially sawed or hewn for smaller poles. For large poles, 
pine is suitable on account of size and straightness ; but pine, partic- 
ularly southern pine and spruce, are not as durable as chestnut or 
cedar. The latter has long life, but is rather too crooked and 


Q44 ELECTRIC LIGHEING. 


knotty for first-class work, where appearance is important. In 
California sawed redwood is recommended. 

Preservation of Timber. — Wooden poles for electrical lines or 
other exposed timber is liable to be destroyed more or less rapidly 
by decay, or by the ravages of various small forms of animal life. 
The chief cause of decay is the fermentation of the sap. When 
located continually under water, wood is hardly affected by decay, 
but may be attacked by the ¢Zevedo navalis, or other animal ene- 
mies. But when alternately dried and wet, or when buried in the 
earth, it is especially liable to decay. ‘Io prevent it various things 
have been tried. 

1. Kyanizing consists in soaking in a solution of about three 
per cent corrosive sublimate (Hg Cl,). 

2. Burnettizing consists in impregnating timber with a 1 to 
8 per cent solution of zinc chloride (Zn Cl,), formerly by soaking, 
but now by forcing solution into the pores under pressure. Oak 
absorbs about 10 and pine about 20 per cent of its volume. 

The trouble with the above processes is the dissolving out of 
the antiseptic salt, and various means have been devised to prevent 
it, such as the Thilmany process, in which zinc or copper sulphate 
solution was first forced into the pores and then barium chloride 
solution to form insoluble barium sulphate (Zn SO, + Ba Cl, = 
Zn Cl, + Ba SO,). The Wellhouse process employed glue and 
tannin, and the Hagen process used gypsum to retain the salt in 
the wood. 

3. Creosoting consists in placing the timber separated by laths 
on cars which are run into a large cylinder closed by heavy iron 
doors. Live steam at 225° to 250° F. is turned on until the tim- 
ber is heated through, and the albumen of the sap coagulated. 
A vacuum is then formed to extract the sap, and finally the cylin- 
der is pumped full of dead oil of coal-tar,a measured quantity 
being introduced under a pressure of about 100 lbs. per square 
inch. The amount of oil is generally from 10 to 20 lbs. per cubic 
foot of timber, the oil weighing 8.8 lbs. per gallon. Besides pos- 
sessing antiseptic qualities, the oil is insoluble in water, and is not 
washed out or displaced by it. The oil usually only penetrates a 
little below the surface, hence this skin should not be removed 
by subsequent work upon the timber. 

Creosoted telegraph poles in England showed no sign of decay 


OVERHEAD CONDUCTORS. 245 


after 85 years.* In this country creosoted railway ties last about 
20 years on the average. Cresoting also protects timber from the 
attacks of the ¢eredo navalis and the “imnoria terebrans. 

4, Carbolining consists in treating timber at a temperature of 
250° F. with an oil called carbolineum avenarius (invented by 
Captain Avenarius). 

5. Vulcanizing is accomplished by heating timber in closed 
cylinders from 8 to 12 hours at 300° to 500° F., and under 
a pressure of 150 to 200 lbs. per square inch. A circulation of 
heated and dried compressed air removes moisture and any water 
that does not take part in the chemical reaction, and combine with 
the woody constituents. This process changes the character of 
the sap so that it does not ferment, and seals up the pores. Tests 
at Columbia University showed an average increase in strength of 
18.9 per cent, in addition to preservative effect. 

6. Applying fztch or tar to the butt of a pole may do more 
harm than good, as it confines the sap, hastening fermentation and 
decay. But, after the pole has been standing two or three years, 
it might be treated in this way, by digging around it. 


N 


rene en and oe 
a 
ee 
SS oe 
J 
ee Ses 


Figs. 183 and 184, 


Poles are 85 to 60 feet long, but are sometimes 100 feet or 
even longer. Those of 50 feet or more are usually set about 
one-tenth of their length in the ground, but for shorter poles or in 
soft earth they are sometimes buried to the extent of one-eighth or 
one-sixth of their total length. In soft ground they should be 


* N, W, L. Brown in Elec. Railway Gazette, October 19, 1895. 


246 ELECTRICE/ICOIING: 


surrounded with a grouting of Portland cement, sand, and broken 
stone, tamped around the bottom of the pole, or the butt of the 
pole may be set in a barrel filled with sand or firm earth. The 
standard practice is to put from 40 to 50 poles per mile, making 
spans from 132 to 106 feet each. About every tenth pole should 





more 
1 
a 


Figs. 185 and 786. 


be guyed laterally, to prevent wind pressure from overthrowing 
them. This is quite likely to happen; and if one pole falls it is 
likely to drag down the next one, and so on fora long distance, 
unless they are supported by side guys at reasonably frequent 
intervals. The guys usually consist of several strands of No. 6 or 


Y 4; 
LL. / a 
Y y Yy 








Figs. 187 and 188. Arrangement of Guys for Turning a Corner. 


8 iron or steel wire, which is more easily handled than the larger 
wire or rods that are sometimes used. They may be made simple, 
as in Fig. 183, or for high poles they have the Y form (Fig. 184). 

Fig. 185 shows wire guy and pole brace. When a pole is to be 
made very secure it is guyed in two directions, or double guyed. 
This adds greatly to the stability of the pole. See Fig. 186. 


OVERHEAD CONDUCTORS. ay 


On curves or at corners the guys should be more frequent 
and > stronger bene» placed’ on the= outer Side of, the? curve. 
Methods of guying suitable for lines that turn a right angle at 
street corners are shown in Figs. 187 and 188. In such cases, or 
where lines come to an end, as in front of an electric light station, 


A B ¢ 





Fig. 189. Guying of Terminal or Corner Pole. 


the last two or three poles should be stronger and more firmly set 
than the others, and may be guyed as indicated in Fig. 189. It 
is also well if the last one or two spans, A Band, B C, are left 
somewhat more slack than usual, in order not to bring too much 
strain on the terminal pole. 

Cross-Arms are of yellow pine or oak, being usually about 34 x 44, 
or 83 x 44 inches for smaller sizes, and as much as 4% x 53 inches 
for the Niagara transmission line. A cross-arm about 3 feet long 
is used for two insulators, about 5 or 6 feet for 4 insulators, and so 
on. The spacing of the pins is about 4 to 6 inches from the ends, 
24 to 30 inches in the middle, and 
12 to 18 inches for the. rest, de- 
pending upon the size of insulators 
and other conditions. 

(ies: cans. Jor, flat 'spots on 
which the cross-arms are placed 
should be cut in the pole before it 
ts setup, Ordinarily these are 
placed about 24 inches, center to 








Fig. 190. Bracing a Cross-Arm. 


center. The cross-arms should be 

fastened to the pole by two bolts or lag screws, placed diagonally 

in order not to split the wood, and are braced by two iron strap 

braces also attached by bolts or lag screws, as represented in 

Fig. 190. The cross-arms should be put alternately on opposite 

sides of the poles so that they cannot be pulled off successively. 
Guard Wires. — Where one set of overhead electrical wires pass 


248 ELECTRIC LIGHTING. 


- 


under another set, the former should be protected by guard wires, 
An arrangement of this kind is represented in Fig. 191, A4C being 
the galvanized iron or steel guard wires attached directly without 
insulation to a cross-arm or to the top of the pole. These guard 
wires serve to prevent any wire that may fall from coming in con- 
tact with the electrical conductors carried on the insulators DE. 

Guard Hooks. — A hook of stout iron wire or a hoop, as indicated 
in Fig. 192, is often attached to the cross-arm to catch an overhead 
conductor, and prevent it from falling in case the insulator, insula- 
tor pin, or tie-wire should happen to break. They are required 
especially on the inside of curves or angles in the line. 

In this connection it may be stated that electric light or other 
conductors carrying high voltage or heavy current should, if pos- 
sible, be put over telegraph and telephone wires, because the latter 
are more likely to fall, not being so well laid or so carefully watched, 


B 




















Fig. 191. Guard Wires. Fig. 192. Guard Hooks. 


and being more numerous. Another reason for this is the risk of 
requiring telegraph and telephone linemen to pass up through the 
more dangerous wires with which they may not be familiar ; whereas, 
electric light linemen would not be injured by telegraph or tele- 
phone wires. 

Insulators. — The problem of supporting overhead wires is some- 
what difficult, since those materials having sufficiently high insulat- 
ing qualities are not very strong mechanically. Glass and porcelain 
are employed almost universally for the purpose, but neither is 
possessed of the great strength that is very desirable in order to 
enable the insulators to stand the heavy stresses to which they are 
subjected. Other materials, such as hard rubber and various com- 
positions of vegetable or mineral matter, have been tried; but they | 
are rarely used except that the latter are commonly employed to 
support overhead trolley wires. 


OVERHEAD CONDUCTORS. 


249 


The advantages of porcelain over glass are that it is less brittle 
and generally stronger than glass, and it is less hygroscopic. On 
the other hand, glass is cheaper than porcelain, and the fact that it 


is transparent enables an internal defect to be 
detected more readily. It also makes the 
cavities in the insulator less likely to invite the 
building of nests by insects. Another differ- 
ence, which is much more serious than it 
sounds, is the fact that white porcelain insu- 
lators more often attract the eye of a boy or 
hunter, and frequently are made to serve as 
targets for stones or bullets. 

Glass or porcelain insulators for electric 
light and power lines have been developed 
directly from those that are employed for tele- 





Fig. 193. “Deep Groove, 
Double Petticoat ’’; Screw- 
glass Insulator. 


graph and telephone service. In fact, there is no substantial dif- 
ference, the only modifications being an increase in size and 


strength to suit the heavier conductors, and 


single petticoat form. 








forms of glass begins. 























form of insulators. 





Fig. 194, Porcelain ‘Oil 
Type’’ Insulator, mounted 


improvement in insulation by lengthening the 
path for leakage of current, secured by adopt- 
ing the double and triple in place of the 


Types of Insulators. — The deep grooved 
double petticoat pattern of screw-glass_in- 
sulator is the ordinary standard, being used 
with insulated wires for lines of 2000 volts. 
his type isoshown in Pig. 193.0) For higher 
potentials the use of porcelain or special 


The present increasing employment of 
high voltages, and the tendency to raise the 
voltage still higher, has brought into use new 


The oil insulator, shown in Fig. 194, is 
mounted upon an iron pin, and provided with 


on Iron Pin. a recess that is filled with an insulating oil. 


There is a “built-up” type of porcelain insulator, being made 
in. parts as is shown in Fig. 195, and the parts burned together 


with a vitreous cement. 


250 ELECTRICMYICGHIING 


For 20,000 volts an insulator made entirely of porcelain was 
designed. Fig. 196 affords a very good idea of this type. In 
Fig. 197 is the~porcelain pin. base 
employed in combination with the 
insulator of Fig. 196. 

The insulator used on the trans- 
mission line from Niagara to Buffalo, 
together with its wooden pin, and sec- 
tion of the cross-arm, is show in Fig, 
198.9 Dhe weaves tend Wtoschermame 
water at two points, where it will not 






PORCELAIN 
PIN BASE 
drip on the cross-arm. 


An interesting insulator is the one 
used by the Telluride Power Trans- 





(ST 


Pe 
= 























Fig. 195. Built-up Porcelain Insu- 
lator with Iron Pin, 
mission Company to 
transmit power 80 miles, 
from Provo to Mercur, 
Utah: . The / pressure, 
40,000 volts, was the 
highest employed up to 
that time (1898) for com- 
mercial lise: gamhio ne oo 
shows the Provo in- 

sulator. 

A still newer type is 
that shown in Fig. 200. 
It is of brown china 
ware with a glass or por- 
celain cone extending 
down around the pin, which is of wood with a porcelain sleeve and 
base. The idea of this sleeve is to make the striking distance 





Fig. 196. 20,000 Volt Porcelain Insulator. 


OVERHEAD CONDUCTORS. 251 


greater, this being of as much importance as that the length of the 
path from the cross-arm to the wire be made long. This insulator 
is 103” in diameter, about 15” high, and weighs about 12 pounds. 









































Fig. 197. Wood Pin with Porcelain Base. Fig. 198. The Niagara Type of Porcelain Insulator, 
Wood Pin and Cross-arm. 


Another feature is the beveled trough around the top, which 
catches all the water at the periphery, and carries it off to one side 
of the cross-arm. 


Insulated Wire for Overhead Lines.— For long-distance trans- 


~~ 


20% 


b 


ELECTRIC LIGHTING. 


mission bare conductors, described at the beginning of this chap- 


ter, are generally employed, even with very high voltages. 


For 


local distribution, especially within the limits of cities and towns, 


& BS Pas 


Fig. 199. Provo Glass Insulator. 





electric light and power over- 
head wires are covered through- 
out with insulating material, to 
reduce the danger of accidental 
contact with persons or with 
other wires or conducting 
bodies. 

The insulation of overhead 
One of 


impervious 


wires is in two parts. 
insulating material 
to moisture, placed next to the 
wire, and the other of some sub- 
stance fitted to resist abrasion 
or like mechanical injury. | 


The inner coating is a rubber compound, or for lower grades 


Before 
this is laid on the wire it is first 


some cheaper substitute. 


tinned to prevent the sulphur 
in the rubber com- 
pound from corroding the wire. 
This inner coating is then 
covered with a hard braid of 
cotton or hemp, woven on to the 
wire, or the wire is served with 
a tape and insulating compound. 
Where the wire is to be continu- 


contained 


ally moist, gutta percha is better 
than rubber, but it 
costly. 


is more 


In the more expensive 
grades of wire the coatings are 
greater than two in number, and 
they alternate, insulating com- 
pound and then braid or tape. 

In Figs. 201-203 are shown 





Fig. 200. 


Locke High Potential Insulator. 


the manner of application of the insulation and the braid. 


OVERHEAD CONDUCTORS. VAST 


Joints in Overhead Lines. — Whether an electrical conductor is 
bare or insulated it is necessary that any joint made in it shall be 
nearly equal in conductivity and in mechanical strength to the 








































































































Fig. 207. Insulated Line Wire. 


rest of the conductor. The ordinary “lineman’s splice” (Fig. 
204) has been the standard practice for galvanized wire iron, in 
telegraph lines; but the use of copper 
wire, both hard and soft drawn, and the 
necessity for better connection with 


heavy currents, has resulted in the Fig. 202, standard Conductor, In- 
sulated for Outside Work. 









































adoption of various special forms of 
jomt. /Ot these the MelIntire joint illustrated in’ Fig. 205 is a 


prominent exarnple. 






, 


de i ) yy» 
Z pany yyw TREES SSS 


ao Fi 
ei 










ley 
N Sy 
if) Ue, if 


ys 












This joint is made by use of a “connector” which consists of 
two tubes drawn side by side out of one piece of copper. The 
internal diameter of each of these tubes corresponds to the ex- 


RSS} == 


Fig. 204, Lineman’s Splice. 


ternal diameter of tne wire to be spliced. ‘The two wires need not 


be of the same size. 


















































Fig. 205. McIntyre Wire Joint. 


The joint 1s made by slipping the wires inside the tubes, and 
then by means of special pliers, twisting the tubes one on the 


D54 ELECTRIC. LIGHTING. 


other ; thus by friction the two wires are bound firmly together. 
Unless required by Insurance Rules, they need not be soldered, 
a great advantage with hard-drawn copper wire as it avoids anneal- 
ing the wire, and the joint more nearly retains the full strength of 
the wire. | 

In the “lineman’s splice” the actual area of contact wire to 
wire is small, and winless well soldered the crevices will afford 
places for starting corrosion, and the resistance will be high. 

The McIntire joint affords plenty of contact area, giving a low 
resistance and being impervious to moisture. This form of joint 
is especially valuable with the aluminum wire that is now coming 
into use. 

All joints made in insulated wire lines should be taped and 
painted with an insulating compound till the insulation over the 
joint is as good as that on the wire of the line. 

Method of Attaching the Line Wire to the Insulators. — The or- 
dinary plan is to take a simple U-shaped tie-wire, place the curve 
of it around the insulator, and wrap up the projecting ends around 


Ue 


Fig. 206. Tying Wire to Insulator, Fig. 207. Tying Wire to Insulator. 


the line-wire. This puts a side pull on the line-wire which objec- 
tionable feature of this tie is indicated in Fig. 206. This might, 
in the case of hard-drawn copper wire, cause breakage, because it 
is quite brittle. 

The standard method now in use is shown in a completed form 
in Fig. 207. A soft copper tie-wire is laid in and around the insu- 
lator groove, in such a manner that one end comes over, and the 
other end under the line-wire; the ends are then wrapped around 
the line-wire. A method of making the tie is shown in Fig. 208. 
When properly made in this way the line-wire is anchored to the 
insulator with no side pull. 

Tie-wires should be the same size as, or slightly smaller than, 
the conductors themselves. This is true even when the line-wires 


GCEERHAAD CONDUCTORS: 


255 


are insulated, and the insulation of the tie-wire should be equal in 


character and thickness to the line-wire that it ties. 


Dead Ending. — When a line ter- 
minates it is dead-ended by taking a 
turn around the insulator and wrap- 
ping it about itself, or by means of 
a McIntire connector. 

Service Connections and Locps. 
— When it is necessary to take a 
tap off to give service, an extra in- 
sulator must be mounted on the 
cross-arm, in order that the strain of 
the service main may not put a side 
strain on the line-wire; for a series 
circuit the line is usually dead-ended 





to the building to be served. In 
this case the arrangement shown in 
Fig. 209 may be used. 


See 


at the nearest pole, and a loop taken me. 










st 





Fig. 208. Method of making Tie. 


Limitations of Voltage. — The maximum voltage that it is possi- 
ble to employ on overhead lines depends upon conditions. In 1890 
a pressure of 5000 volts was considered to be very high, but gradu- 






MAIN LINE 






nit 
i 















Fig. 209. Method of making Loop Connection. 






ally the apparatus and methods have been improved until 40,000 or 
even 60,000 volts is now regarded as commercially practicable. 


256 ELECTRIC LIGHTING. 


fod 


The electrical maintenance of such a circuit depends entirely upon 
the insulators, since the wires are usually bare, and the poles even 
if made of wood should never be depended upon for insulation, 
especially at such high voltages. 

In a paper before the American Institute of Electrical Engineers,* 
Mr. C. F. Scott gave the results of experiments on several lines, 
and pointed out that the loss between wires by leakage directly 
through the air rose rapidly above a certain voltage. In Fig. 210, 
which shows some of these data, it will be noted (curve 1) that the 
loss between two No. 28 wires 48 inches apart was 500 watts at 
30,000 volts, each wire being 
1040 feet long. This is far too 
great . for commercial work, 
since the waste would amount 


2000 





Losses between Wires 
of Different Sizes 
Frequency 133, Smooth 
Armature, Length 1040" 








1800 





















oe aa te {Na,28 Wires, 48pare 
Apes eee IT tO wa DOUG Fo Ola Ke wee peimiic: 
1400 eee | With larger wires the loss de- 
og Lae SIS eS [ea Se creases  SiorMexamn plc RimmeM mye 
Heb EAE 8 the leakage for two No. 8 
eae Te Ish tah Vio oMilcs (hes samencisianicam Dake 
800 AAA tA is only one-fifth as great at 
oe EER EEE AE 30,000 volts, being 100 watts 
tH AEH for the same length. When 
400 EECA No. 7 wires, rubber-covered, 
OTS ST te ae eaearesusedarcuiver) at bemicssmis 

WERMMGEEACON Ho 

aes r++ ~~ «practically nil at 30,000 volts, 








9 ina el 
Coa em ee 60 7 and only becomes 50 watts at 

Fig. 210. Loss between Wires in Air. 60,000 volts, or .25 kw. per 
mile. The substitution of still 

larger conductors secures a further reduction in this leakage 
through the air, so that it can be kept within reasonable limits even 
at 60,000 volts. A transmission line in California, which is de- 
siened to operate at this pressure, employs aluminum wires one inch 
in diameter, which should give very little air leakage, even though 
they are bare. When the distance between wires is increased, the 
loss is diminished, as shown in Fig. 211. It is also a fact that the 
leakage depends upon the wave form of the pressure, being greater 
with peaked than with flat topped waves, since the maximum volt- 


* Transactions, June 30, 1898. 


OVERHEAD CONDUCTORS. DO 


age is higher in the former case. The percentage of humidity in 
the atmosphere, or even a fall of rain or snow, does not materially 
increase this loss through the air. 


3000 





Loss on Circuit with Wiresat 
Different Distances. 
Frequency 60, Slotted Armature, 
Weston Wattmeter. 

Wires 15,22,35and 52 ins. apart 
































aie 
CEEEE ECA 
t+ 







LE ee 
OSE oem 
aH-pe eh 


P| | | 
Si at 


————TTCOrLCOSCS~S 
OA Om cunlo w20m ct eh oe oO 400 1445 48525556 8160 
Thousands of Volts. 






Fig. 211. Loss between Wires in Air. 


Lightning Arresters are required in almost all cases in connection 
with overhead conductors. The principal forms in use, and the 
manner of using them, were described quite fully in Vol. I., pages 


425 to 438. 


ill 
at 


GENERAL SPECIFICATIONS FOR ORDINARY POLE LINE 
CONSTRUCTION. 


(2000 vo.Ts.) 


Poles to be of best quality cedar or chestnut, round or octagonal, 
as specified. Height to be approximately thirty (30) to thirty-five 
(35) feet. Diameter of base to be ten (10) inches. Diameter of 
top to be about six (6) inches. The poles to be straight and knots 
closely trimmed. Tops to be chamfered. 

Gaius to be cut square with the axis of the pole and with all 
other gains, and to be accurately made to fit cross-arms, so as to 
bring the cross-arms nearly flush with the pole. 

Painting. Poles which are specified to be painted to have the 
lower six and one-half (64) feet, including the base of the pole, either 
creosoted or painted with a heavy coat of tar paint or equal. (This 
is not to be done if the pole is “green” or sappy.) The roof of the 


258 ELECTRIC LIGHTING. 


pole to be painted with three (3) coats of best quality white lead. 
All gains to receive two (2) coats of best white lead previous to the 
introduction of cross-arms. Lower shanks of pins to be painted 
with white lead before being inserted into cross-arms. Cross-arms 
to be thoroughly painted with two (2) good coats of mineral paint 
put on with a brush. After the poles are erected and wires in 
place all the poles specified to be painted with two (2) coats of best 
quality dark-green mineral paint. 

Guy-Stubs and Anchor Logs to be used where the pole needs 
side guying on a sharp bend, or wherever the country does not pro- 
vide a more convenient way to guy them. These anchor logs or 
guy-stubs to be of proper dimensions, depending on the size of the 
pole and weight of the line. 

Cross-Arms to be thoroughly sound, straight-grained timber, 
of southern pine, and free from knots. The arms to be of 
requisite length, to be sawed true and square, and up to the dimen- 
sions specified. The top side of the cross-arm to be chamfered 
throughout the whole length, with the exception of eight (8) inches 
at the center, where the arm fits the gain. Cross-arms to have 
holes bored of spacing and size for pins, as specified or shown on 
drawings. Cross-arms to be screwed to the pole by two (2) 2 inch 
galvanized iron bolts extending entirely through the arm and pole. 
Under the head and nut of each bolt a galvanized iron washer, not 
less than 24 inches in diameter, shall be placed. Bolts to be stag- 
gered. (This construction refers to cross-arms carrying heavy 
wires and large number of same. On light lines lag screws are 
sufficient.) 

Iron Fittings to be of good quality best refined wrought iron, 
which would conform to good bridge specifications, to be thor- 
oughly galvanized. Galvanizing to be subject to a test. Cross- 
arm braces to be used on all the cross-arms having four (4) or more 
pins. The braces to be secured to the pole with a lag screw, and 
to the cross-arm with carriage bolts of sufficient length to go 
through the braces and arms. Galvanized iron washers to be placed 
under the head of all bolts, nuts, and lag screws. 

Pins. All pins to be best quality, sound, clear, split locust, 
free from knots and sapwood. Pins to be of standard dimensions, 
which are governed by the size and weight of the insulators, etc. 
The threading and tapering shall be neatly and accurately cut, 


OVERHEAD CONDUCTORS. 259 


showing the full thread, and shall accurately fit the insulator. Each 
pin to be secured to the cross-arm by a sixpenny galvanized iron 
wire nail driven straight through cross-arm and shank of pin. On 
all curves pins to be bolted by galvanized iron bolts. 

Insulators. Insulators as per sample to be used, to be sound, 
strong, free from fins, having threaded holes accurately molded 
and of uniform size. To be double petticoated, made of glass, and 
subject to a break-down test of 6000 volts, from a source capable 
of delivering five (5) amperes at that pressure. 

Guy-Rods. Anchor guys shall be attached to galvanized iron 
guy-rods. These rods to be from 6 to 8 feet long, 3 inch in diam- 
eter, provided witha galvanized iron washer 2 inch thick and 3 
inches square, with 3 inch hole for reception of the rod. 

Wire-Rope Fittings. All wire-rope fittings, such as thimbles, 
guy-clamps, rings, sockets, shall be of first-class quality of wire- 
rope fittings, equivalent in every respect to those manufactured by 
the Roebling Company or Washburn & Moen. To be galvanized. 

Lightning Rods. Every tenth pole to be supplied with a light- 

ning rod made of No. 6 galvanized iron wire, carried at least one 
foot above top of pole, and secured to same by heavy galvanized 
steel staples made of No. 4 (B. and S. gauge) wire. These staples 
shall be 24 inches long. The wire shall be carried down the pole, 
and thoroughly buried in the ground at the base of the pole, with at 
least two hand turns. 
_ Guy-Ropes to be made of good flexible quality galvanized 
iron, and to be composed of one or more strands, depending on the 
stress to be borne by the guy. To conform to good specifications 
for elongation, twist, and breaking. 

Construction Details. The line shall be located by measuring 
off and placing stakes for pole location at distances of 120 feet as 
an average. Such stakes must be placed as nearly in line as possi- 
ble. In case of obstacles, the pole should be located as near the 
stakes as possible. In the distribution of the poles, the strongest 
and heaviest poles shall be placed on line corners, while the best- 
looking shall be distributed throughout the town, or in the front of 
residences. The length of the pole shall be proportioned to the 
contour of the country, so that the wires may be strung without 
abrupt changes in level. 

On straight lines all poles shall be set in the ground to a depth 


260 PLECTRICOLIGHTING 


of at least six feet, unless otherwise specified. All poles shall be 
set perpendicularly on straight-line work. On curves, poles should 
be set with an outward rake. 

The holes shall be dug sufficiently large to admit the butt of 
the pole without hewing’; and after the pole is set, the earth shall 
be returned and thoroughly tamped around all the base of the pole. 
Tamping shall be done in the proportion of three tampers to one 
shoveler. Upon curves the poles must be laterally guyed. 

Every eighth pole to be laterally guyed on both sides, and on 
steep hills every pole shall be head-guyed in both directions. 

The two end poles of each line shall be head and laterally 
guyed. On long spans the poles shall be head-guyed both ways, 
and side-guyed in both directions. 

«Y”’ guying to be used in all cases. 

Where it is difficult to get good setting for a pole, same to be 
set in “sand-barrel’’,or concrete, to be approved by the engineers. 

In cases where poles are set in rock, pole to be hewn to fit an 
approved iron shoe, which is to be securely bolted to rock. Shoe 
to be painted inside with two coats of white lead before pole is in- 
serted. Outside of shoe to be smooth, and hydraulic cement to be 
placed on top of rock on which shoe is set. 

Guys to be fastened to poles by means of galvanized eye-bolt, 
fitted with galvanized washers under head and under nut of bolt. 

Placing of Cross-Arms. On straight-line work, the cross-arms 
to be placed on alternate sides of succeeding poles. On long spans 
the cross-arms of terminal poles shall be placed opposite the long 
section. Double cross-arms to be used on all abrupt changes in 
direction and also on end poles. 

At the end of lines the arms of at least the last two poles shall 
be placed on the side facing the terminal of the line. On curves 
the cross-arms shall face towards the middle of the curve. 

Long spans of 200 feet shall be head-guyed, and if possible 
side-cuyed in both directions. 

Tying of Wires. Line wires shall be tied in a manner as ap- 
proved by the engineers. , 

Joints. All joints to be made either with a McIntyre sleeve or 
a Western Union splice, and to be thoroughly soldered, taped, and 
bound with cord. 

Guard Hooks. To be placed on each cross-arm on sharp bends. 


OVERHEAD CONDUCTORS. 261 


Guard Wires. To be placed wherever wires cross above or 
below another line. 

Binding Wire. Binding wire to be used to secure wires on all 
insulators. Wires to be of first-class insulation, solid copper wire, 
two gauge numbers smaller than the line wire. No binding wire 
smaller than No. 8 B and S. gauge to be used. 

Excavation. All excavating and filling for pole line to be done 
by contractor ; also felling of trees, bushes, and all blasting, grad- 
ing, etc. Trees and bushes to be trimmed so that no branch can 
come in contact with the wires. All removing and replacing of 
fences or other structures which may be found necessary for locat- 
ing pole line to be done by the contractor. 


262 ELECTRIC LIGHTING. 


CEVA? PD BAR texas 
UNDERGROUND ELECTRICAL CONDUCTORS. 


Tue branch of electrical light engineering that is the greatest 
in magnitude, and involves the largest expenditure, is that which 
relates to the designing, laying, and maintaining of a large system 
of underground conductors. In no other department of electric 
lighting are the practice and results so variable. For nearly ten 
years after electric lighting was first introduced, the distribution of 
a current was effected almost entirely by overhead wires, the only 
important exception being the Edison Underground System, first 
laid in 1882, and generally employed by most of the low-tension, 
direct-current systems in the larger cities of this country, and in 
many places abroad. Since 1890 the popular objection to the use 
of overhead electrical wires has grown, and wherever possible has 
demanded the substitution for them of underground conductors. 
The enormous expense of making the change, as well as the almost 
utter lack of experience with buried high-tension circuits, made this 
a most formidable problem at first. As is usual in such cases, 
extraordinary methods were devised for overcoming the apparent 
difficulties. It has been found, however, that very simple con- 
struction, provided it is of good quality, insures the practical suc- 
cess and permanence of underground conductors. In fact, 
alternating current and arc-lighting circuits of 1000 to 7000 volts 
are commonly laid in underground conduits, and do not give much 
more trouble than low-tension wires, including those employed for 
telegraphic and telephonic purposes. The essential elements of an 
underground system of conductors are, first, the conductor itself, 
which is almost invariably composed of copper ; second, the insula- 
tion, which may be either a complete covering of non-conducting 
material, or simply points of support; and third, the mechanical 
protection, which usually takes the form of a tube or conduit, and 
must be particularly strong in order to withstand the severe con- 
ditions to which it is exposed. 


CONDERGROOUNDI ELECTRICAL CONDGCTORS. 263 


In some instances, especially in Europe, iron-armored cables 
are laid directly in the earth, without any conduit to protect them. 
The armor, which is relied upon for mechanical protection, consists 
of a spiral winding of iron or steel wire, like that of a submarine 
cable, or a spiral wrapping of iron or steel tape, with overlapping 
joints. In either case there is a certain amount of flexibility 
which a conduit does not possess, enabling the cable to pass around 
obstacles and adapt itself to the various underground pipes, etc., 
that are often very numerous in large cities. Moreover, the iron- 
armored cable would occupy much less space than an equivalent 
conduit. In some underground conductor systems the cables are 
drawn in after the conduits are built, and in others the conductors 
are put in the sections before they are laid, or are built in at the 
same time. 


FORMS OF UNDERGROUND CONDUITS. 
. Drawing-[n Systems. 


IRON. 


Wrought-iron pipes. 
ri i vay cement lined. 
“wood lined. 
Cast-iron pipes. 
aes trourns. 


Mm RW DN 


EARTHEN WARE. 


6. Terra-cotta pipes, single or multiple duct. 
6c 66 troughs 66 66 6 


CONCRETE, 


8. One or more ducts formed in a mass of concrete. 


WOOD, 
g. Wooden pipes. 
10. « troughs. 
11. Fiber pipes. 
Solid or Built-In Systems. 


12. Edison and other underground Tube Systems. 
13. Crompton and other naked Conductor Systems 


Wrought-Iron or Steel Pipes, similar to gas or steam pipes with 
screw or other connections, is the strongest and one of the most 
satisfactory forms of conduit ; and it has been extensively adopted, 


264 ELECTRIC LIGHTING. 


particularly where its rather high first cost is not a serious objec- 
tion. Its advantages are great strength.to resist the severe strains 
due to the pressure of the earth, often aggravated by unequal set- 
tling. It is also well adapted to withstand blows of pick-axes, 
shovels, etc., to which conduits are exposed during subsequent ex- 
cavations of the same ground. Wrought-iron or steel pipes require 
to be of less thickness, and therefore occupy less space than any 
other form of conduit. They can be joined by screw or other con- 
nections which are most secure, and can also be made water-tight. 
Such a pipe can be bent to a reasonable extent without breaking 
or opening the joints ; whereas with almost any other form of con- 
duit the unequal settling of the ground, which is almost certain to 
occur, is likely to crack or break it. 

The disadvantages of wrought-iron pipes are their somewhat 
high first cost, and the fact that they are made of conducting 
material, which will cause a ground connection if the insulation of 
the wire is injured. It is doubtful, however, if non-conducting con- 
duits, such as earthenware, are really better for underground con- 
struction. Ifa difficulty occurs in the insulation of the wire, the 
incidental insulation afforded by the conduit is hardly sufficient to 
enable the circuit to be worked properly. The moisture which 
would almost always be present would produce a_ sufficient 
“oround’’ to render it undesirable and probably dangerous to 
employ the conductor. In most cases it would be just as well, and 
would enable a fault to be more quickly detected and located, if a 
“dead ground,” ie., low-resistance ground connection were made 
immediately. In fact, with high-tension circuits in non-conducting 
conduits, it is important to have the lead sheathing of the cables 
that are ordinarily used well grounded throughout its entire length, 
otherwise a defect in the insulation, or simply the electrostatic 
charging and discharging which takes place with alternating cur- 
rents, render it dangerous to touch the lead sheathing. 

Wrought-Iron Pipe in Hydraulic Cement. — This is used to 
quite a large extent, the ordinary construction for this conduit 
consisting in digging a trench in the street, the size depending 
upon the number of pipes to be laid. The bottom of this trench, 
after being carefully leveled or graded, is covered with a layer 
of good concrete 2 to 4 inches deep, and the sides are braced 
with plank. A suitable mixture for this purpose is composed of 





UNDERGROUND ELECTRICAL CONDUCTORS. 265 


two parts of Rosendale cement, three parts sand, and five parts 
broken stone. Broken stone to pass through a one and one-half 
inch mesh. ‘The concrete is well rammed into place, and a layer 
of wrought-iron pipe is laid upon it. The diameter of these pipes 
depends upon the size and number of cables that they are to re- 
ceive, the standard being 8 or 4 inches in diameter, and 4 inch 
thick. The pipes are in 20-foot lengths, and are joined by means 
of a tapering or vanishing screw thread coupling, forming a joint 
which is water- and gas-tight, and can easily be made as the pipes 
are laid in place. When the first layer of pipes is in place, spaces 
between and around them are filled with concrete, ihe distance 
between. the | pipes as) 

usually one-half to three- eet eaee aie 

quarters of their diam- Vinee ‘ 

eter, the thickness of the 
concrete on the sides 





being about the same 
amount. The concrete 
is filled in over the pipes 
to a depth about half 
of a diameter, and then 


/ 


1% APPROX 








1 


17g PLANKS 


another layer of pipes is 
laid and packed around 
with concrete as before. 
After the last row is in 
place, a covering of con- 
crete from 2 to 8 inches 
in thickness is spread over it, and a layer of yellow pine plank 2 
inches thick is laid upon this. The chief object of the latter is to 
serve as a protection against the tools of the workmen in case of 
later excavations. Experience has shown that men will dig down 
through concrete, but will turn aside from the wood. 
The following construction is standard in this kind of work 
being used in New York City. (See Fig. 212.) 
The thickness of cement all around the bunch of conduits is 
4 inches. The boards cn the side of the trench are 14 inches, 
and there are 2-inch boards on the top. Three-inch wrought-iron 
reamed pipe is used, which is superior to the ordinary commercial 
pipe, in that it is reamed after being rolled to insure that there are 








Ys Yi 


2A BP RO et 





Fig. 212. Cross-Section of lron Pipe Conduit. 


266 ELECTRIC LICHIING. 


- 


no blisters or rough points on the interior of the pipe. The pipe 
is dipped in a tar to prevent rusting. Fig. 212 shows a 12-duct 
construction. This is larger than the average. 

The pipes are laid at 41 inches between centers, both between 
the rows and the pipes in the rows. This adds up, for total con- 
duit construction, about 14 feet deep by 2 feet broad. 

A cement formula that has been found sufficient is, Cement 
1 part, sand 2 parts, and 3 inch broken stone 3} parts. 

It is evident that this construction is extremely substantial and 
well adapted to withstand the most severe mechanical forces, being 
also gas- and water-tight. The iron pipes are found to last very 
well, the action on their external surfaces being very slight. They 
rust internally to a considerable extent, being exposed to moisture 
and air; but it would take a long time for them to be corroded 
away entirely. Even should this occur, a smooth hole will be left 
in the concrete, and would still serve as a conduit for the conduc- 
tors, and would last almost indefinitely. 

The use of asphaltic concrete instead of that containing cement 
has been proposed ; but it would be still more expensive, and would 
not seem to offer a compensating advantage. [he manholes, hand- 
holes, and methods of distribution employed in connection with 
this form of conduit, will be described later, since they are quite 
similar for all types. 

Wrought-Iron Pipes Lined with Wood have also been used; but, 
as already stated, it is doubtful if a non-conducting conduit is 
especially desirable. But the wooden lining would at least serve 
as a means of preventing the chafing of the cable as it is drawn in, 
and might in that way prove a valuable feature. On the other 
hand, it might tend to corrode the lead covering of cables as de- 
scribed later under “ Wooden Conduits.”’ 

Wrought-Iron Pipe, Cement Lined.— This form of ducts usually 
consists of eight-foot lengths, made of thin (No. 26, B. W. G.) 
sheet iron, riveted every two inches, as represented in Fig. 213. 
The pipes are lined with a layer of pure Rosendale cement, % of an 
inch thick, no sand being used. The internal diameter is 3 inches, 
making the external diameter approximately 43 inches. The out- 
side of the pipe is tarred to prevent rusting. The interior surface 
of the cement is extremely smooth ; in fact, it has a polished ap- 
pearance, so that there is not an excessive amount of friction to 


UNDERGROUND ELECTRICAL CONDUCTORS. 267 


interfere with the introduction or withdrawal of the cables. Each 
section weighs between 40 and 950 pounds, and is therefore easily 
handled in laying and joining. ‘These pipes are laid in cement in 
a manner similar to that described in the case of plain iron pipe, 
but the thickness of the pipes is somewhat greater. This form of 
conduit can be laid rapidly. Twenty ducts with a total of 12,820 
feet of pipe were put down in a single day in St. Louis. The 
gang of men required to do this work were 86 concreters, 52 
laborers, 6 bricklayers with 6 helpers, and 6 overseers. The 
trench in this case was already open; but the work included the 


















































Fig. 213. Cement-lined Iron Pipe. 


building of 13 manholes and 4 handholes. In another case a gang 
of 108 laborers, 40 concreters, 5 bricklayers, and 5 helpers, with 
7 overseers dug a ditch 1157 feet long, put in 5 ducts, and filled 
in the trench in a single day. These may be considered as ex- 
traordinary ‘“runs,’’ an average of 500 duct feet complete being 
the usual result of a day’s work. Figs. 214 and 217 show con- 
duits in course of construction. 

Cast-Iron Pipe Conduit.— These are similar to the plain 
wrought-iron pipe already described. In order to have equal 
strength the cast-iron would have to be thicker than the wrought- 
iron, so that the cost would be as great or greater; and since the 
former occupies more space, and is heavier to handle, there is no 
great advantage in employing it. Cast-iron, however, lasts longer 
in the earth than wrought-iron. 

Cast-Iron Trough Conduits. — Various forms of this construc- 
tion have been used, a prominent example being the Johnstone 
conduit. This consists of shallow troughs of cast-iron in lengths 
of about 6 feet, which may be laid directly in the earth, as repre- 
sented in Fig. 215. The cables are then run along in the trough, 
and covers of cast-iron are placed over the troughs, the two being 
bolted together. This construction possesses the advantages that 
the cables are laid directly in place without being drawn in, so that 
there is less liability of their being injured ; and still more impor- 
tant is the fact that the cables are accessible at any point for 


a7 


rae 
-~ 


LPL 
SHH 


rH 
HHI 
Sas 


ELECTRIC LAGH LIANG. 
































Fig. 215. 


Cast-Iron Trough Conduit. 


Se 
KK 


\ 


@ 





UNDERGROUND ELECTRICAL CONDUCTORS. 26° 


inspection, repair, or branch connection, by simply removing one 
of the sections of cover, which are very easily unbolted and 
handled. For this reason the system is particularly well adapted 
to distribution, in contradistinction to transmission of current on 
feeders or trunk lines. Unfortunately the cost is so high as to 
be almost prohibitive. In some cases the troughs are completely 
filled with an insulating compound after the conductors are laid in 
them, thus excluding moisture, gases, chemical agents, etc., that 
might otherwise leak in and injure the insulation. Such construc- 
tion, however, comes under the head of “built-in ’’ and not “ draw- 
ing-in ’’ systems. 

The self-induction of alternating current conductors laid in iron 
pipes or troughs must be overcome by twin or concentric cables. 

Earthenware Conduits. — Various forms known as “terra- 
cotta,’ “ glazed-clay,” and “hollow-brick tile”’ conduits are manu- 
factured and_ used. 
The ordinary single- 
duct form, illustrated 
in Fig. 216, consists 
of an earthenware 
pipe 18 inches long, 
the internal diameter 



















































































































































































Fig. 216. Glazed Clay Conduit, 


being usually 3 inches, but smaller and larger sizes are made also. 
The thickness of the walls is about 2 inch, the external form being 
octagonal, as shown. These are made of clay burned moderately 
hard, and glazed inside and out. They are laid in a trench upon a 
| bed of concrete from 3 to 6 
inches thick, being placed side 
by side with spaces of 4 or } 
inch between them, which are 






filled with cement mortar. 
Single-duct conduit joints being 
self-centering, are simply sock- 
etedjone into thesoether, The 
Figkbi7). Giased Clay’ Conduite conduit is built up in layers, 

with the pipes breaking joints 
very much like the bricks in an ordinary wall. The concrete con- 
sists of 1 part cement, 2 parts sand, and 5 parts screened gravel, 
broken stone, or broken brick ; the stone to pass through 14-inch 


i SL 
oe | 






ZE 





















































270 ELECTRIC. TIGHTING 


mesh ; the cement and sand to be first thoroughly mixed dry, then 
a sufficient quantity of water added to make a rather soft mortar ; 
the gravel, stone, or brick to be added afterwards, and thoroughly 
mixed. The gravel, stone, or brick should not exceed one inch in 
its greatest diameter. The conduit is usually protected on the 
sides and top by a layer of concrete at least three inches thick ; 
but in some cases the concrete is omitted, when two one-inch yel- 
low pine boards are placed over conduit. Great care should be ex- 
ercised in laying the ducts so that the alignment is sufficiently good 
to enable the conductor to be easily drawn in and without injury. 
This is generally secured by inserting a round stick or mandrel of 
wood through the ducts as they are laid. The mandrel, which fits 


Pos ol (a a <--9'—-» 


FE rap se Z 
ZOOL EFL GA if Lf tty fb 06: 
LOG PEL ESL 12.GEG Legis 
COLOECLELOUAE ES, VIELE Yt) 





















LIELAS PA GLACE, 
hie piplippiiis as 
SLOLLLLGIESPIEE 


3 
ie 











DTH. 





Wl 





T FO 


Fig. 218. Multiple-duct Earthenware Conduits. 


the bore of the pipes quite closely, insures that they are in line 
while being filled around with mortar, and there is a disk of rubber 
on the end of the mandrel that acts to scrape out any mortar or 
dirt that may happen to get into the duct. The axis of each pipe 
is slightly curved, and they should be laid so that the convex side is 
upward, in order that the joints shall interfere as little as possible 
with drawing in the cables. The advantage of this form of conduit 
is its simplicity, cheapness, and the fact that any desired number 
of ducts may be put together; and to avoid obstructions under- 
ground, the geometrical form of the conduit may be modified by 
different arrangement of the separate pipes, and it is quite easy to 
slightly change its direction, so that it may be carried around ob- 
stacles. 


UNDERGROUND ELECTRICAL CONDUCTORS. DAA 


Multiple-duct earthenware conduits are similar in general form 
and method of laying to the single-duct construction just described. 
The difference lies in the fact that each unit contains two or more 
ducts, as represented in Fig. 218. In this way space and the labor 
of laying are somewhat economized. Multiple-duct conduits are 
centered with two dowel pins at each joint, and then wrapped with 





Fig. 219. Joints in Multiple-duct Conduits, 


a six-inch strip of asphalted burlap, or with a six-inch strip of damp 
cheese cloth, and then given a coating of cement mortar, as shown 
in Biss 219, 

Earthenware Trough Conduits consist of clay troughs, either 
simple or with partitions, as represented in Fig. 220. The usual 
dimensions are 3 or 4 inches square for each compartment, with 








Fig. 220. Earthenware Trough Conduits, 


walls about 1 inch thick, the sections being 2 to 4 feet long, and 
weighing about 85 pounds each for the 2-foot four-duct trough 
shown. To cover the top trough a sheet of mild steel, No. 22 
gauge, is bent to fit over the sides to hold it in place, and is cov- 
ered over with concrete. When the latter has solidified, it acts as 
aroof to the top layer of ducts, even though the sheet of steel 


rusts entirely away. 


PAG ELECTRIC LIGHTING. 


‘ 


Ducts formed in Concrete. A method of constructing a con- 
duit consists in partly filling a trench with concrete in which 
continuous longitudinal holes are formed to serve as ducts after 
the concrete has hardened. One plan is to use collapsible man- 
drels of wood or metal, which are placed where the ducts are 
desired and then filled around with concrete. When the concrete 
has solidified the mandrels are made to collapse, and taken out in 
pieces. Another means of producing a similar result is to employ 
tubes made of thin sheet zinc or iron, which are placed in the 
concrete as it is filled in, and are just strong enough to stand the 
pressure to which they are sub- 
jected It istexpected that the 
thin metal will soon corrode 














away, but the ducts will remain 
in the mass of concrete. 

































= SSS — 
SL ° e nod 
ZZ =a Wooden Pipe Conduit. — A 
—S—__ simple and cheap form of. con- 
Fig. 221. Wooden Pipe Conduit. duit consists of pieces of wood 


3 to 6 feet long and 43 inches 
square, through which a round hole 3 inches in diameter is bored 
longitudinally. These are laid side by side in layers, as shown in 
Fig. 221, to form a conduit with any desired number of ducts. 
At the bottom and top a layer of plank is laid to protect and hold 
in place the separate pieces. There is a projection at one end of 
each section which fits 
into a_ corresponding 
recess in the next sec- 
{100 ease lidreatec: sin 
Fig. 222. This conduit : 
is often called p ump 4 Fig. 222. Wooden Pipe Conduit. 
log conduit. 

Wooden Trough or Box Conduit. — Ducts about 3 inches square 
are made of horizontal boards and vertical partitions of yellow pine 
one inch thick. This may be laid in convenient lengths of about 
12 feet or may be built along continuously. The wood should 





= 





‘ 





have been previously treated with creosote or dead oil to preserve 
it, as described on page 244, and the whole exterior of the conduit 
is coated with tar. 

The objection to this or any form of wooden conduit is the 


UNDERGROUND ELECTRICAL CONDUCTORS. 273 


fact that the decay of the wood tends to form acetic acid which 
attacks the lead sheathing that is usually applied to underground 
conductors. This produces a white scale, irregular pits, or a white 
efflorescence on the lead, and is likely to cause much more damage 
than the dark brown uniform coating which sometimes forms on 
lead but stops further action. The lead acetate resulting from the 
first-described action is often decomposed by carbonic oxide chan- 
ging it to lead carbonate, and setting free the acetic acid which 
again attacks the lead and so on. The decay of the wood and 
formation of acetic acid are intended to be prevented by the 
treatment with creosote or dead oil, but this may not be entirely 
effective. Wood is good for temporary work, for it will last about 
10 or 15 years, and can be easily cut into for changes and repairs 
or side connections. 

Fiber Conduit consists of pipes made of wood pulp, having 
about the same thickness as cast-iron pipe. S/zp joint conduit for 
electrical subways is 3 inches inside diameter, and has short sock- 
ets on the ends, one to fit inside the other, keeping the lengths 
centered, and making it much easier to lay than a mere butt joint. 
It is laid in cement lke iron pipe. The screw joint pipe will form 
a tight line, and is used for running underneath the lawns of 
private houses, or underneath the streets of villages, the importance 
of which will not warrant the cost of building electric subways. 
Being used in this manner like iron pipe, it can be cut with a saw 
or lathe tools. It is said not to corrode nor change in dimensions 
with varying temperature. 

Ordinary conduit construction is illustrated in Fig. 223, the 
conduits in this case being terra-cotta, but may consist of other 
kinds of pipe. 

It is hardly necessary to lay conduits below the frost line as 
they are not likely to be injured by frost. When laid in concrete 
they should be at least 2 feet below the surface, and when clay 
pipes are laid bare, 3 feet, to avoid crushing by the weight of the 
heavy vehicles above. : 

Edison Tube System is a very good one for distribution, and 
for extending to new territory section by section, being much 
more convenient in this respect than conduit and cable. 

The 7ude consists of one or more conductors contained in and 
insulated from an iron pipe. In the three-wire system which is in 


OCs ELECTRICALICHIING 


- 


general use, three copper rods are placed in each tube. The 
system is a sectional one, and each tube is as complete when it 
leaves the factory as is a rail from the rolling-mill. Like a rail 
it only needs to be joined to other similar units to become part of 
a continuous line. These tubes may make as many bends as cir- 
cumstances call for, while a conduit must run practically straight 
from manhole to manhole. 

In the three-wire system of distribution the conductors, whether 
overhead or underground, are divided into two classes. Feeders 





Fig. 223. Terra-Cotta Conduit under Construction. 


which run from the stations to the centers of distribution con- 
stitute the first class. Jazus radiate from centers of distribution, 
and loop the ends of the feeders together, constituting the second 
class. All taps to supply customers with current are taken from 
the mains. Tubes are therefore divided into Feeders and Mains. 
A main has three insulated conductors of the same size. A feeder 
has two principal conductors and a smaller conductor to serve as a 
neutral wire. A feeder also has three insulated cables of 7 strands 


UNDERGROUND ELECTRICAL CONDUCTORS. AGS 


of No. 19 B. W. G. wires each. These small cables form inde- 
pendent circuits from the station to the point of distribu- 
tion, and enable the voltage at the outside end of the feeder to 
be read in the station. Hence these lines are called pressure 
wires. ce. Mipgaa 

The conductors are all copper rods, 20 feet, 4 inches long, and 
project from 2 to 34 inches from each end of the pipe. The 
pipes are lap-welded steam pipe, of full weight. 

In’makine Uipeastubesthe ends of the» copper rod are first 
chamfered and tinned. The pipe is thoroughly cleansed on the 
inside. Each rod is wound separately with a prepared rope, and 
the three rods so wound are made into a triangular bundle and - 





Fig. 224, Construction of Edison Tube. 


wrapped with a fourth rope. See Fig. 224. This bundle of rods 
bound with rope is slipped into the pipe. When the rods are in 
position the pipe is placed on end, and a melted special compound 
is forced in from the lower end. As the compound rises it dis- 
places the air, and thus prevents air bubbles. The ends of the 
pipe are closed with a rubber plug. As soon as the insulating 
material is cooled the completed section of the pipe is carefully 
tested, the tube is then painted to preserve the iron from rust, and 
is ready for shipment. 

In order to complete the system, there is needed a means of 
joining the ends of the conductors in the consecutive tubes, and 
of insulating and protecting such a joint when made. 


276 ELE CTRICGUIOATING: 


In Fig. 225 it will be seen that the two ends of the pipe enter 
an egg-shaped casting through two water-tight sleeves at either 
end of the oval. The copper rods forming the conductors are 
joined by coupling joints consisting of short pieces of flexible 
cable with sockets cast on each end. ‘These sockets are drilled to 
fit easily over the rods which the joint is to connect. After the 
connectors are in place they are thoroughly soldered to the ends 
of the conductors, thus making an electrical joint. The covering 
of the egg-shaped casting is bolted down on the lower half, and by 
means of a small hole on the top of the casting, the whole of the 
box is filled with melted insulating compound, which surrounds and 
insulates the copper rods, the joints and the tube ends. This 









































Zo\N IN 












































Fig. 225. poate ae Edison Tubes. 


compound does not grow brittle on cooling or with age, but 
remains somewhat plastic even at freezing temperature. The hole 
in the casting is closed with a cast-iron cap. 

Coupling-boxes are made also in the form of elbows and tees, 
to provide for all possible conditions, such as service wires, turns 
in the line, etc. The ball end that may be attached to the end 
of the tube, and the socket that it fits into, permit a considerable 
variation in direction if desired, there being a range of 18 degrees 
on either side of the mean position. 

Branches to the consumers’ premises, or as they are commonly 
called the servvzces, are short lengths of tube which tap the main 
line by means of a three-way or service box. These boxes are 
made for right and 45 degree angles. A four-way box readily per- 


UNDERGROUND ELECTRICAL CONDUCTORS. OTT 


mits of two services being taken from one joint. A form of box is 
shown in Fig. 226. 

Mains are so placed in the ground that the positive and nega- 
tive conductors are on one side of the vertical plane through the 




































































Fig. 226. Branch Connection of Edison Tubes. 


center of the tube, while the neutral or balancing wire is on the 
other wmocem ip 221.) Ihesside of (the tube which. the neutral 
is on is called the inside, because the main tube is so placed that 
che; neutral ‘copper is nearer to the curb line: ~ The feeders are 
laid symmetrically, 
with the right hand 
conductor as the 
tube leaves the sta- 
tion being the posi- 
tive. Services are 
never taken from 
the; fecder-lines: 
This requires that 
at some center of distribution the feeder be split up and branched 
out, or what is the same thing that it be connected up to one or 
more mains. The feeder enters a distributing-box, and the con- 
ductors are connected to three copper rings. From these rings, as 
a source of potential, mains are led out through fuses to supply, by 





FEEDERS MAINS 
Fig. 227. Cross-Section of Edison Tubes. 


278 ELECTRIC CHTING. 


means of the service connections, the surrounding district. From 
the rings of this box the pressure wires return to the station. This 
box not only serves as a center of distribution, but also as center 
of equalization of pressure between the different parts of the sys- 
tem. Fig. 228 shows the arrangement of the distributing-box. In 
some cases the fuses are replaced by heavy copper strips. 
Installation of the Tubes. ‘Yhe trench in which the tubes are 
to be laid should be as a rule 30 inches deep, and 20 inches wide 














SS 





SSS 


srt 


mh 





te 








































































































SoS 


— 



































































































































































































































































































































































































































































































































































































































































































































Fig. 228. Distributing Box. Edison Tube System. 


at the bottom, this giving a trench wide enough for two tubes. 
As is shown in Fig. 229, the main is laid nearer the curb to facili- 
tate the taking off of taps or services to the houses; such ser- 
vices running under the sidewalk, and entering the cellars of the 
houses. If there is only one line of main on a street, it is laid 
about six inches higher than the feeder, should there be one, in 
order that services may be taken off for both sides of the street. 

The system may seem burdened with details; but when it is 


UNDERGROUND ELECTRICAL CONDUCTORS. 279 


considered that the system takes the current from the dynamo, 
and delivers it to the consumer, that the tube is the equivalent of 
three ducts in a con- 

duit and three insu- Z777.X 


lated cables,andthat 7/7) 
its flexibility is great, 7 : 
j 






we see that it pos- / 
yy 
sesses advantages. jj 


/ 





For many years it 
was the most impor- 
tant underground 
system. 

Naked Conductor 
Systems.— There 
areat least two meth- 
ods by which bare wires or rods may be operated in underground 
conduits. One in which the wires are supported on insulators of 


oO 
© 


Fig. 229. Edison Underground Tubes. 


glass, porcelain, soapstone, etc., in the conduits ; and the other in 
which the conduit itself is of an insulating material. 

The former method is used somewhat extensively in Europe, 
entirely, however, for low pressure electric lighting service. 

In this use of bare conductors care must be taken to prevent 
the undue access of moisture into the ducts, and especially to 
prevent the flooding of the conduits. 

The Crompton System of bare copper strips has been exten- 
sively used in England. The conduit, or culvert for a three wire 
system is shown in Fig. 230, and will be 
seen to be a trench lined with concrete, 
and covered with a layer of flag stone. 
It is usually built under the sidewalks. 

FP eo80 © Cramnront Conduite The conductors are copper strips 1 to 

14 inch wide, and 1} to } inch thick. 

These strips rest in notches on the top of the porcelain or glass in- 

sulators, which are carried on an oak timber built into the concrete 
walls. 

To prevent the leakage from moisture it is necessary that the 
number of the supports of the strip be reduced toa minimum. To 
accomplish this, about every 300 feet there is an enlarged hand- 
hole for a straining device which takes all the sag out of the 











CONCRETE 





280 ELECTRIC LIGHTING. 


strips, and makes it possible for them to place the insulators about 
50 feet apart, instead of every 10 feet. This device is shown in 
Fig. 281. The conductors are, when stretched, clamped by the 


set screws W. The ends of the strips are then joined by the 
Glan pac. 


















SS SN SX XAQX®GC N Y 
\RAVEMENT\ J, 
WX QQ Ww y 






















































eT | 
oa ES S B 


Es 


Fists mee ie eer en eine ine el He sere 
SUCONCRETE 15:22" 







se eps Se era MSE Sore ENS 
oy Eke Sass Sar DISS eer nen eee oe 
CoN Age oy et as - Suet poner. tees 









Fig. 231. Stretching Device in Crompton System. 


In order that the insulators may be reached for inspection and 
for cleansing, a hand-hole is placed over each set of insulators, — 
that is, about every 50 feet, — and these boxes are utilized for the 
service connections. Rubber-covered cable is generally used for 


ae 


this service, and it is 
attached to the copper 
strips. by a clamp like 
Ceinsiiows2) ls 

The Kennedy System 
is a modification of the 
Crompton, using solid 
porcelain bench-like sup- 


ports set directly on the 
bottom of the conduit, as shown in Fig. 252. 


The Callender Solid System. In the Callender solid system 
a series of cast-iron troughs are laid along the bottom of a trench 
excavated in the street. In the trough the requisite number of 









Li 
Fig. 232, Kennedy Conduit. 


UNDERGROUND ELECTRICAL CONDUCTORS. 281 


cables are strung, supported at intervals by insulating pieces fixed 
in the troughs. This protection is found to be necessary, from 
the fact that the insulating compound with which the trough is to 
be filled is never absolutely hard, but 
behaves like a viscous fluid ; and the 
cables would otherwise gradually set- 
tle. 

The cables are insulated, and with 
the melted asphalt that is poured into 
the troughs, makes an expensive in- 
sulation. A cast-iron cover is placed 
over the top of the trough. A section 
of this system is shown in Fig. 2338. 

Electric Light Cables for use in con- 
duits are of two classes, according as the insulation is or is not 
moisture proof. In the first class the insulation is rubber, or bitu- 
men, and the lead covering is for the protection from chemical and 
mechanical injuries. The second class is insulated with jute, 
hemp, or paper impregnated with oil, wax, or resinous compound. 











Fig. 233. Callender Conduit. 


The lead covering of this cable is absolutely necessary for its 
electrical integrity, on account of the hygroscopic nature of the in- 
sulation. The latter types are much cheaper, but need the test of 
time to demonstrate their value. 

Rubber is made durable and the cost reduced by being com- 
pounded with litharge, French chalk, barytes, etc., which strengthen 

it mechanically, and render it less liable to decompose. 
| Vulcanized rubber is now generally used, it being mechanically 
stronger, more flexible, and capable of standing higher temperatures 
than pure rubber. The process consists in mixing a small amount 
of sulphur with the rubber, and subjecting it to a temperature 
of 250 to 200 degrees F., while keeping it under pressure. 

Fearing the action of the excess of uncombined sulphur on the 
copper, the conductor is tinned before the insulation is applied. It 
will be seen that for a cable of many strands the wires themselves 
must be tinned. The Hooper process may be applied, consisting in 
first covering the cable with a layer of pure rubber, and then with 
a layer of rubber highly pigmented with oxide of zinc, and then 
to put on the vulcanized rubber. The requisite amount of sulphur 
can be determined so closely that the excess may be very small, so 
that this separating layer may not be necessary. 


282 ELECTRIC OYGHUIING. 


The general method of insulating a cable is to first wrap round 
it one or more layers of pure rubber tape, which are put on spirally ; 
the direction of the spiral being reversed for each successive layer. 
On top of this, rubber compound is applied in two or more separate 
coatings. cach coat being put on by passing the partially formed 
core with two strips of rubber compound, one above and one below 
it, between a pair of rollers which fold each strip half around the 
core, and press the edges of the two strips together so as to make a 








Fig. 234, Lead-covered Stranded Cable. Fig. 235. Duplex Cable with Fibrous Insulation. 














UKE DIGG C 
Ene 
Sk i) Coe 


Rubber 
Compound 






sear 
4 

AAs 

OY, 


Fig. 2386. Underground Cable. 


(lip N72 Layers 
mee,* of Braid 


agi Rubber 





Fig. 237. Underg,sund Cable. Fig, 288. Underground Cable. 


good joint along each side. When a sufficient number of layers of 
rubber compound have been put on to give the requisite thickness, 
the core is tightly bound with a spiral wrapping of prepared rubber 
tape, and then vulcanized. After this it is tested; and if it proves 
satisfactory then it is taken to the taping and braiding machines, 
where the external covering of tapes and braiding is put on. 

Lead covering. These cables are generally incased for their 
mechanical protection. This may be done by drawing the cable 
into a lead tube, which is then drawn through a die and made 


UNDERGROUND ELECTRICAL CONDUCTORS. 283 


to fit the core tightly; or the lead cover may be put on in a 
hydraulic press, the hot lead being forced out through an annular 
die around the cable. 

The Siemens cable is one of the second class, the conductor 
being wrapped with jute, and impregnated with a special bituminous 
compound mixed with heavy oil, and is then covered with lead. 

Paper cable. A similar cable is of paper wound on in strips 
spirally over the conductor; and as each strip is applied, it is 
passed through a die which presses it into a compact mass. The 
Gore sis athene diicdpate ae temperatures of 250° FE. to expels the 
moisture from the paper, and immersed in a bath of compound, 
from which it passes directly to the lead-covering press. 

With either of the methods of lead covering by a press, it is 
difficult to test the soundness of the lead, unless the cable is im- 
mersed in water for a long time. For this reason some makers 
prefer to use a manufactured lead tube, which can be tested under 
pressure to see if it is sound, and then the cable is drawn into it. 

Figs. 254 to 238 represent the general form of cables. 

As one type of special cable, Fig. 289 shows a lead-covered, 
three-conductor cable, such as is being used for three-phase trans- 
mission of current at 6600 
volts, from the 96th-street 
station to various sub-stations 
in New York City. The con- 
ductors are each equivalent to 
a No. 0000 A. W. G. wire, and 
are composed of thirty-seven 
strands of tinned Lake copper. 
Around each conductor is a 
Hooper core containing no 
sulphur ; the total imsulating 







INSULATION’ 


—JUTE 
FILLING 


INSULATION 


: te STRANDED 
wall around each conductor is conbucTGR 


#3 of an inch. Together with Fig. 239. Three-phase 6600 Volt Cable. 

the jute fillers these conduc- 

tors are twisted with a lay of about 20 inches.. The whole is then 
covered with a second insulating wall of 34; inches’ thickness. Lead 
covering 1 inch thick is then put on. The covering is an alloy of 
lead and tin, the percentage of tin being 21 to 8. The total 


diameter of this cable is 23 inches. 


284 ELECTRIC LIGHTING. 

This torm of insulation is popularly called sp/zt znsulation for the 
reason that it is substituted for a cable having 4$ of an inch around 
each conductor, and none around the bunch of three. Should the 
latter form of cable be used, it would perhaps be one quarter inch 
greater in diameter, and would cost at least 25 per cent more. The 
“split insulation,” it will be seen, offers the thickness (4$) of insu- 
lation needed between conductors, and the same thickness between 
conductors and the lead sheath as in the old style. 

Each individual conductor before assembling is tested, after 


d 


24 hours’ immersion in water, with a break-down test of 15,000 
volts, sustained for an hour, after which the insulation resistance 
must measure 500 megohms per mile. When the cable is com- 
pleted, and laid in the ground, a break-down test of 20,000 volts is 
applied for an hour, and at the expiration of this test the insulation 
resistance must measure 1000 megohms per mile. 

Concentric Cables. The Ferranti mains are concentric cables 
made in rigid lengths of 20 feet, and a cone sleeve is used to make 
the connections. The main consists of two copper tubes, one en- 
tirely within the other; they are insulated from each other by 
brown paper steeped in black wax, the outer tube being covered 
with the same material, and 
the whole inclosed in an 
iron tube. 

A common form is that 
of an inner stranded con- 
ductor, and an outer con- 
ductor formed by a layer of 
spirally-wound wires. The 
jointing of these cables is 
made by upsetting the 
outer wires and clamping 
them between washers, and 
connecting the washers by 
a strip of sheet copper ; 





Fig. 240. Concentric Cable. the inner conductors can 

be soldered, or clamped 

and then soldered. This kind of cable is shown in Fig. 240. 
Even if a straight soldered inner and outer joint is made, the 
joint is so bulky that a coupling-box is clamped on. It is provided 


ONDEXRGKOGND ELECTRICAL ‘CONDUCTORS. 285 


with rubber washers at a, or these chambers are filled with 
asphalt, to make them water-tight, and the main chamber filled with 
compound. Such a box and joint are shown in Fig. 241. 

There is this difficulty in the use of concentric cables, that it is 
not possible to ascertain the condition of the insulation between 
the two conductors without cutting out the dynamo, transformer, 
















































































Fig. 241. Concentric Cable Joints. 


or other apparatus in the circuit ; and therefore the insulation can- 
not be tested while the circuit is working. This is a serious dis- 
advantage, as with separate cables a continual test may be kept on 
the circuit, which will often give warning before the fault is suff- 
ciently developed to prevent the circuit being worked. Thus an 
opportunity is given to localize the fault and repair before any inter- 
ruption of the lighting takes place. 

———Joints in Cables. — Joints in solid conductors are generally 
made by scarfing the ends and soldering; then the joint is tightly 
wrapped with a serving of copper wire, or a split sleeve put on, the 
joint being again soldered. The flux must contain no acid. 

Stranded cables are made solid by dipping the ends in solder, 
and treated as above. 


286 ELECTRIC. TIGHTING. 


In multi-conductor cables the jointing. is more difficult on 
account of the lack of space, and the necessity of getting the 
insulation between the conductors. 

The joint of each conductor is insulated by rubber and com- 
pound tape to the desired thickness. 

The lead covering is replaced by a piece of pipe previously 
slipped on the cable, being soldered to the lead sheath, or a wiped 
joint may be applied. The object in both cases is to get a water- 
tight joint. 

In some cables, after this lead is in place, holes are punched in 
it, and hot compound poured into the interstices which have been 
left. The holes are then soldered up. 

Manholes. — The various systems in which the conductors are 
drawn into iron, earthenware, or wooden conduits usually require 
manholes to be located 




















not more than 200 or ee 
eile om sere ae - an ats 
300 feet apart, the cables Z£—____ SS - 








ITELLEEELEEEEZEZEEE__TTEZ_E 


3 PAY ul 
being pulled from one to , | | | I 
Wk) 


ihe vother=by aieatis= Olt Se = za 


| | | wl 

















rope. These manholes 








ordinarily consist of Mi aT 
chambers of brickwork | il il il 
of the general form rep- ) 

ea in Fig. 242. . y= a @ 
They should be provided “|| Go a9 
with two covers,- the 
lower one being screwed 


| 


Mi 
i 


Tun 
Ht 


ih 


A 





















































| 
| 





— 
down on a rubber gasket Ke 
so as to be water-tight, 


and the upper one rest- 

ing hee a its place, itl Mild Zi V/ U/l 
BiH being, Aretheanthithe Fig. 242, Cross-section of Manhole. 
surface of the street, as indicated. 

According to the kind and sizes of the duct, the form of the 
manhole will change slightly. Fig. 243 shows a manhole used in 
connection with vitrified multiduct conduit. Fig. 244 will give a 
good idea of the interior of a manhole looking down into it from 
the stecet: 

{n dry or porous soils the bottom of the manhole is some times 


UNDARGROCND ELECTRICAL CONDUCTORS. 231 


= 


wy Pry RELI EPL LLM 
= me 


LLL LL 
MLL ne a Geers mena era os WHtuW 

TAIN YZ. ANZ WA \] Ea Gs TT NENA ZEN NYA. YO: 
WAAL ee dd ee SE 
A Vid elegans [ee] oe eee) CT UP UT Kx. 
VEL ONC) eA ee ee ed BZ oto 
YHAPARADTOI ADT SR Lae See ai BAZ 
MLL. LL, Wh 
LLL Ae ae | ae | a | | a | | ee eek | ee [eee | eee [eae | eel eel | 7 

LAH r 


LMI 
Whee Qa Oe DES eS ee eee ee eee enue) y 


8 a I. AN 


OL Hi ee 
OLA L111 
peo OOOOlE 

A 7/7 oo ///// 


EK Gavooooooooooo 
= HIS LITE roaeemes ea | oOwook€ [CO eres 
SSS 


















———— = En . Soe 
Se re Bommmncee|| i OoIWooIe i Sais Pana es a ae a 
) aaoaare Ss ——————— Sse GY 
ey 
VA ZAG ieee eee ee ee TWA Y 


ea 



































Ao “is 











Wom t+ —T PIES 














Z2 


Yj 





~ ay 








Woon 





Eig. 243. Brick and Iron Manhole, 


288 “ FLECTRIC DIGHIING. 


- 


left out so as to drain it; when this is not feasible a sewer con- 
nection is make to accomplish the same result. 

The typical manhole adopted for the New York subways is 
shown in Fig. 245, being drained by a pipe P leading to the sewer. 








COE 
ps Hy 


AM 



































Fig. 244, View into a Manhole. 


Fig. 246 is a view of the iron-pipe conduit used extensively 
in the city, showing a service box in place, being practically a 
small manhole with 
side connections for 
the buildings. Fig. 
247 shows such a box. 
When the number of 
the ducts is not large, 


LIGA ‘© O asin local distribution, 
Z 


St Ne ES ei 


QU: the manholes and ser- 


vice. boxes become 
mere hand-holes. 
Drawing in the 
Conductors. — Since a 
duct is entirely empty 
when built, and is usually from 200 to 800 feet long between 
manholes, it is necessary to employ some special means of getting 





ESSAY 











Fig. 245. New York Subway Manhole, 


yy 
y 


/; 
Uy 


Wy 


ven DB 
L{ 
EZ: A 


if Z, IRN 
z, is 2; AS 


UNDERGROUND ELECTRICAL CONDUCTORS 


nay Va i 
t 





f A 


Yi 
Wy 


Fig. 246. Iron Pipe Conduit. 


Ne 


\\ 


= 





i) 


ZA Te. 
BS e . 
Sars Wags 
Se ig 


’ 
p - Hi 
s - 
- . 7 
7 - 


a BILE 7 RS 
é 2 eS RNY é 
Lg SS = ore 
GL wees 
AAS na Lies 
oy = ge 
(ea el eee 
‘7 RN 4S, 7 
25S SS e 
LOI SS RN AS 
“Le SS Ke, 
4 
‘ RNY ea 
Z _ ese 






ea 
PER RN 


: 


A 


Fig. 247. Service Box for Terra Cotta Conduit. 


x y/ 
Ul his 


yy, 
Uiiy 


Yi 





289 


290 ELECTRIC LIGHTING. 


a rope through it in order to draw in the cable. One plan is simply 
to push through a steel tape or wire, which is provided with a 
rounded metal head to prevent the end from catching in the joints 
between the pipes. By means of this tape or wire, a small and 
then a large rope may be pulled through the duct. Another 
method is the so-called “rodding” of the ducts, a 20-minute ope- 
ration, consisting in inserting one after another into a duct, short 
rods of wood or steel, about 3 or 
4 feet long and ? inch in diameter, 
which are connected together by 
screw or bayonet joints,as indicated 
in Fig. 248. When a sufficient 
number have been joined to reach 
from, onesmanhole to the next 4 
small rope is attached to a ring in 
the last one, and the rods are then pulled through from the other 
end, being unjointed as they come out. A larger rope may then 
be drawn through, after which a steel scraper and a brush should 
be pulled through the duct in order to 
clean it, and remove any stones, tools, 
etc., that are often found in it and would 
be very likely to injure the cable. These 
are illustrated in Fig. 249. 

After the duct has been cleaned prop- 
erly, the end'of the cablevig atrached ito qu isa mee tt aula 
heavy rope which has been drawn through Fé 
the duct by attaching it to the cleaning implements. In attaching 
the cable to the rope, care should be exercised to avoid bringing 
undue strain on the copper conductor or its insulation during the 
operation of drawing in the cable. This may be done by putting a 
conical metallic head on the end of the cable, or by winding several 
iron wires spirally around the last foot or two of the cable, and form- 
ing these into a loop to which the rope is attached. For hard pulls 
and curved pipes the end of the cable is served, after removing 
about 18 inches of the lead and the insulation. The strands of the 
cable are then fanned out, and divided into four groups, and passed 
through a shackle as shown in Fig. 250; they are bent back on 
themselves, and bound tightly with spun yarn or wire. If the pull 
is to be extra hard, an iron wire may be also put through the 






















































































ONDERGCRKOOUND LLECTRICAL CONDUCTORS. 291 


shackle, and driven through the lead sheath. This gives an excel- 
lent hold on the cable, distributing the strain over all the conduc- 
tors, as well as to the lead covering. 

































SHEATH 


























‘YARN SERVING 
Fig. 250. Attachment for Cable to Rope. 


Having attached the cable through a swivel to a strong rope, it 
is drawn into the duct by means of an apparatus shown in Fig. 251. 
The cable unwinds from the drum D, as it is drawn by the winch W. 
It is evident that the cable should be somewhat smaller than 









®0000000 





Fig. 251. Winch for “ Drawing in” Cable. 


the duct through which it is drawn, but the margin need not be 
great. For example,.cables 23 inch in diameter can be drawn 
through the standard 38-inch ducts. When several cables are to 
be put in the same duct it is much better to draw them all in at 
the same time; but it is possible to draw one into a duct already 
containing others, provided there is space enough. It is also pos- 
sible to withdraw one or several cables from a duct without serious 
injury to them, in case repair or change becomes necessary. 
Methods of Distribution from underground conduits constitute 
one of the most serious problems in connection with them. The 
main or trunk lines may be provided for by the various forms of 
conduit that have been described, but these do not readily allow 
branch connections to be made at frequent intervals to supply indi- 
vidual buildings. It is decidedly objectionable to complicate and 


292 ELECTRICWLIGEHTING: 


- 


weaken the construction of the main conduits by having side con- 
nections, so that the best plan is to keep those intact, and provide 
a subsidiary duct or conduit into which the conductors required for 
local distribution are run at one of the manholes. Such an arrange- 
ment is shown in Fig. 252. 
















) 
= Ny 
= 

ee 





a 
























A 
(NN 


Wi! 





Fig. 252, Hand-hole Distribution. 


In Figs. 253 and 254 are shown iron subsidiary service boxes 
for use in connection with terra-cotta conduits. 

The Edison system of distribution is well shown in Fig. 255 
which illustrates also a distributing box and service box. 





Fig. 253. Iron Service Box for Pipe Conduit. 


The house vault, back yard, lamp-post, housetop, hand-hole 
methods of distribution are easily seen to refer to the way by 
which the service cable passes from the subway to the building. 
Street arc lamps may be supplied as indicated in Fig. 256. 


UNDERGROUND ELECTRICAL CONDUCTORS 293 


In Baltimore there is a complete system of distribution, shown 


in Fig. 257, and consisting of two separate parts 





Fig. 254. lron Service Box for Terra-Cotta Conduit 

























\\ ar 
alt |= a 
wank ===} fee TD be 
C= . =) Z: ZA 


i ‘€ 


IQ 


ZS py 
aan mM 4 ‘ 






































Fig. 255. Edison System of Distribution 


For high-tension distribution there is a wrought-iron pipe duct 
with service boxes to transformer pits, consumers, etc., being en- 
tirely a subway, and entering buildings through cellars. 


4 


294 ELECTRICUYCGHIING 


For low-tension mains there is a conduit system of wrought- 
iron tubes, cement-lined tubes, or terra-cotta duct, leading to 
pole terminals situated on each block, and thence overhead to 
consumers. 


VENTILATION OF UNDERGROUND CONDUIT SYSTEMS. 


Considerable difficulty has been experienced in satisfactorily 
ventilating subways carrying electric light and power conductors. 
When these systems were first introduced they were made as 
nearly as possible air-tight and the covers of manholes hermetically 










QSSRQQAAYRAYA 


A 


WF 
yy 
\ A 
My), 
/} // 
\ 


QA 
Yj 1, 


RRA 

SY 

NS 
KY 
~ Vi Yj 

SIL 

—w. 

ES 

So 

=> 


SS 


QS 
\ . Ne \ \ 
x i 
\ 

Xs 


SAX 
WS 
— he 





Fig. 256. Lamp-post Connection. 


sealed. The porosity of the material forming the walls, etc., 
defeated this end, and allowed gas to enter the different parts of the 
system where it mingled with air. The blowing of a fuse or a 
spark due to some other cause would often ignite this mixture of 
air and gas, and destructive explosions sometimes resulted. 

To avoid this danger pumping equipments were arranged to re- 
move the air from the subways. This at first seemed effective, as 
it tended to keep the air in the subway. in motion, but it also in- 
duced gas to enter, due to the partial vactium caused. 

After abandoning this scheme a new arrangement was introduced 
known as the blower system. This was based on the idea that if 


UNDERGROUND ELECTRICAL CONDUCTORS. 295 


an air pressure was maintained in the subway it would prevent out- 
side gas from entering. The fallacy of this hypothesis was soon 
evident, owing to the law that if two gases are separated by a porous 
diaphragm, even though greater pressure is maintained on one side 


SAAR 


je AA 


Fig. 257. A Complete System of Distribution. 


ey 


ea 




















































































































than the other, the gases will still mix. The brick walls in the 
subway acted in this case as the diaphragm ; and explosions still 
occurred after the introduction of this ventilating system, although 
of less frequency and violence. Tests showed, moreover, that the 


296 FELEGTRICSLEIGILING 


- 


blower system produces practically no pressure except within a 
radius of a few blocks from the station. 

It was then decided to employ gangs of men who would visit 
various manholes, remove the covers, and let the subway at these 
points become ventilated. Owing to the excessive cost of these 
methods they were finally abandoned. The ventilation of manhole 
covers was then considered. The chief objection to ventilating 
covers was that they would allow the subway to fill up with water 
and dirt, and thus cause trouble. This proved, however, not to 
be the case in practice ; for late experiments show that the dirt and 
water accumulated in very small amounts, and that only a small 
force of men was needed to remove such accumulations. The 
amount of gas which collects in the conduits proves relatively 
much less than with the blower system, and the total saving is very 
considerable. 

The escape of gas from the gas mains still constitutes a source 
of much annoyance and danger, and even at the present time the 
precautions above mentioned have not proved sufficient to entirely 
eliminate the dangers of explosions. 

For further information regarding Underground Electrical Con- 
ductors reference may be made to the following works : 


Electric Transmission of Energy by A. V. Abbott, Second Edition, N.Y., 
1899, 

Electric Distribution by Kilgour, Swan.and Biggs, London, 1893. 

Electric Light Cables by S. A. Russell, London and N. Y., 1892. 

Localisation of Faults in Electric Light Mains by F.C. Raphael, London 
andoNa ys. L898: 

Ligues et Transmissions Electrigues par Weiller et Vivarez, Paris, 1892. 


Peon RLECTRIC CRC 297 


CHAPTER XIV. 
THE ELECTRIC ARC. 


Definition. — The electric arc is the phenomenon of light and 
heat occurring when an electric current persists in maintaining 
itself across an opening made in its circuit. When of short 
duration and of disruptive character it is known as a spark; the 
term arc being used to designate a continued discharge across a 
bridge of conducting vapor. 

History. — The spark was first observed by Volta in 1800, in 
which year, too, Sir Humphry Davy discovered the particularly 
bright spark between charcoal points separated in air or under 
liquids, and exhibited it before the Royal Institution with the aid 
of a battery of 150 elements. It was not until 1808 that Davy, 
with a battery of 2000 elements, was able to exhibit the first true 
arc, an extended flame nearly four inches long, before the Royal 
{nstitution. This discharge was maintained between horizontal 
charcoal points, and owing to the current of heated air which is 
created, assumed a bow or arch shape; hence its name of “arc.” 

The intense brilliancy and whiteness of this light resulted in 
wide-spread efforts to utilize it practically ; and numerous improve- 
ments followed, chief of which was Foucault’s introduction in 1843 
of gas-coke carbons to replace those of charcoal hitherto used. 
Another early step in advance was Grove’s use of the salts of 
sodium and potassium to steady and increase the length of the arc. 
The application of the arc to practical purposes was often at- 
tempted, but the cost of electrical energy generated by a primary 
battery is so high that no commercial success was accomplished 
until the dynamo had been developed.* 

General Features of Arc.— An arc may be maintained by either 
direct or alternating current. Under ordinary circumstances the 


* Vol. L., pp. 8-17. 


298 ELECTRIC TIGHIING. 


- 


two electrodes must be brought together before being separated to 
establish an arc, otherwise several thousand volts pressure would 
be required to strike across the air-gap in the first place. As soon 
as the separation of the terminals commences, the spark, which 
tends to form at any break in a circuit, vaporizes a portion of the 
material of the electrodes, thus establishing a bridge of conduct- 
ing vapor through which the current flow is maintained. The 
concentration of energy in a small space produces an intense heat, 
which vaporizes the electrodes rapidly, so that a highly refractory 
terminal must be employed to avoid its rapid consumption. More- 
over, the intensity of light given out by the arc depends on the 
temperature to which the electrodes can be heated without being 
vaporized, therefore a highly refractory substance like carbon best 
fulfills the requirements. 

Appearance. When an arc is sprung between two carbon rods 
placed vertically one over the other, and kept about one-eighth of an 
inch apart, a constant current of about 5 to 15 
amperes will produce a stationary condition after 
a few minutes burning. If observed through 
smoked glass, or, better still, if the image of the 
arc and carbons be projected upon a white screen 
by a lens, it will be seen that both carbons tend 
to become bluntly pointed, because oxidized away 
by the heat ; but the positive carbon, which is 
usually the upper on account of its emitting 
more light, will have a hollow, or “crater,” at 
the tip. This may be .04 inch deep and 2. inch 
across under average conditions. This is the 
hottest and most luminous portion of the car- 
bons, attaining a temperature of approximately 
8500° C. as Violle proved, breaking it off and 
dropping it into a water calorimeter. The in- 
tense heat thus generated can be realized when 
the melting point of platinum is considered, 
which is 1,775° C. The negative electrode ex- 
hibits no tendency to become hollowed, and remains pointed. In 
fact, the carbon particles burned from the tip of the positive car- 
bon tend to deposit in the shape of a point or nib on the negative 
carbon, which is much cooler and less luminous than the positive. 








oes yi ays 


258. Appearance 
of Arc Light Carbons. 


THAME LECTRIC ARC. 299 


Both carbons appear luminous some distance away from the tips, 
this being especially noticeable on the positive. If the carbons 
contain impurities, these may generally be seen in beads near the 
tips, to which they often work their way to be instantly volatilized. 
Between the carbon points is the arc stream proper, which assumes 
a bow shape even when the carbons are vertical, owing to the 
magnetic action of the earth’s lines of force on the current. The 
inner portion of the arc stream consists of a violet hub, probably 
of incandescent carbon vapor, surrounded by a thin non-luminous 
portion where the carbon combines with the oxygen of the atmo- 
sphere in dark flame to form carbon monoxide (CO). This is 
enveloped in turn by a layer of luminous flame in which the 
carbon monoxide burns to carbon dioxide (CO,). The magnified 
image of an arc on a screen will show occasional carbon particles 
flying from the positive (which on the screen seems to be the 
lower carbon) to the negative, while other particles are thrown off 
into space by the action of the heated air. 

Noise. Under favorable conditions the arc is perfectly quiet, 
but emits a hissing sound like frying if the current exceeds the 
proper value for the length of arc employed. 

Odor. A distinct odor is noticeable close to the arc, especially 
in damp weather, probably due to the presence in small quantities 
of hydrocyanic acid gas. Besides this, carbon monoxide and diox- 
ide as well as nitric oxide are usually present ; but none of these 
gases is given off in sufficient quantity to be injurious where the 
voltage of the arc does not rise above 505 in air. 

After some minutes burning, it will be observed that both 
carbons waste away, the positive as a rule being consumed in the 
open direct current arc about twice as fast as the negative, the 
ratio depending on various conditions. For this reason the car- 
bons must be fed together by hand or by some automatic device, 
otherwise the length of the gap would increase until its resistance 
exceeded the power of the generating apparatus to maintain a 
current through it. 

Physics of the Arc.— Under commercial conditions direct 
current open arcs usually consume about 10 amperes at 46 volts 
or 450 watts. Thus nearly one-half k.w. of energy is con- 
centrated in heating up the small extent of the crater and arc, re- 
sulting in the production of the very high temperature of 3500° C, 


300 ELECTRICULIGH LIANG 


taken to be the boiling-point of carbon. That carbon is vola- 
tilized in the arc is undoubtedly a fact. The surface of the crater 
has the appearance of boiling; the hissing noise occurring with 
excessive current density is similar to that produced by violent 
boiling of water, and may result from the same cause, though 
carbon, like arsenic, vaporizes directly from the solid state. Car- 
bon consumption goes on in a vacuum, although at a slower rate 
than in air, and the vapor thus formed condenses on the sides of 
the inclosing chamber. These facts all go to show that carbon is 
actually evaporated. Such being the case, the temperature of the 
surface of the carbon would naturally remain stationary at this 
boiling-point, like the temperature of boiling water at atmospheric 
pressure, whatever the heat applied. The temperature of the 
negative carbon, except at its extreme point, is considerably lower 
than that of the positive: ” The difference 1s, due*to thesfach nat 
the larger part of the energy is transformed into heat at or near 
the surface of the positive carbon. This is evident from the rela- 
tive appearance of the two electrodes and is demonstrated experi- 
mentally by measuring the distribution of potential between the 
carbons. The most reliable observations show that about 40 volts 
drop occurs between the positive and the arc stream, with only 
21 volts in the stream and 23 volts between the stream and the 
negative carbon. 

The temperature of the space between the carbons may be 
much higher than that of the surface in the same way that steam 
can be superheated above the point at which it is evaporated, there 
being, in fact, no limit to the possible rise in temperature. Since 
the current is conducted by the highly heated vapor present, it is 
to be expected that such a conductor will be heated by the passage 
of a current the same as a solid or a liquid. 

Theory. — It is evident that the amount of carbon vaporized 
at the positive crater forming the arc stream will vary with the 
current, therefore the resistance of the arc, which varies inversely 
with its cross-section, varies inversely with the current. In this 
respect the arc is totally unlike solid or liquid conductors, whose 
resistance is independent of the current, other conditions remain- 
ing the same. Hence Ohm’s law in its general form is inapplica- 
ble to the arc stream. 

The fact that the phenomena at the arc are more or less rever- 


THE ELECTRIC ARC. 301 


sible, since the vaporized carbon can again be converted into the 
solid state by condensation, points to the existence of a counter- 
electro-motive force, and since the temperature of the vaporization 
“is constant, or nearly so, the counter electro-motive force should 
also be constant, which appears to be the case. Physicists have 
long sought to isolate and determine this experimentally, and it 
would seem that such a definite physical problem could easily be 
solved ; but there are peculiar difficulties, which up to the present 
time have rendered all methods and results questionable. There 
are great difficulties connected with retaining the arc, whose car- 
bons are constantly changing, at a constant condition, and a long 
time is required to permit the arc to assume a stationary state. 
Further, the depth of the crater, and consequently the true length 
of the arc, is very hard to measure at any given moment. Again, 
the resistance varies with the length of the arc and in some 
inverse ratio with the current. Add to this the difficulty of 
securing pure carbons whose density, electrical conductivity, and 
heat conductivity are uniform throughout, and the utter impossi- 
bility of retaining the counter-electro-motive force after the cur- 
rent which induces it has ceased to flow, and the difficulties be- 
come more apparent. By indirect methods an approximate value 
of 85 to 391 volts has been arrived at for arcs of 10 amperes and 
45 volts and pure carbons. The indications point to a counter- 
electro-motive force at the arc, variable with the current and other 
conditions. In fact, it is very likely that it consists of a combina- 
tion of two or perhaps more separate electro-motive forces ; one 
~ due to the volatilization of the carbon, another due to the thermo- 
electric effect at the positive carbon, and perhaps still another 


been said, it seems probable that whatever tends to raise the boil- 
ing point of carbon will likewise raise the voltage required to 
maintain an arc, a conclusion confirmed by experiment. Increase 
of atmospheric pressure, other conditions being constant, increases 
the arc voltage. Similarly we should be able to reduce the voltage 
by lowering the vaporizing point of the crater, an effect which is 
found to result when more volatile substances, such as the salts of 
the earth metals, are introduced, usually in the form of a core. 
Resistance. — The resistance of an arc, like that of any other 


302 ELECTRIC LIGHTING. 

conductor, increases with its actual length, and diminishes with its 
cross-section. The length of an arc usually given is the apparent 
length ; that is, the distance from the edge of the crater to the tip 
of the negative. The true length is, of course, the distance from 
the dottom of the crater to the tip of the negative. A case may 
easily be imagined where, owing to the varying depth of the crater, 
the apparent length might be diminished yet the actual length 
increased. Failure to distinguish between these two is apt to 
result in misleading conclusions. The cross-section of the arc 
varies at different points between the carbons, since it has a ten- 
dency to spread out from electric repulsion, which causes its 
section to be greatest about midway between the carbon points. 
The arc stream tends to spread out farther as the carbons are 
drawn apart. The area of the crater, which is, of course, one end 
of the arc stream, has been found by Ayrton to vary approxi- 
mately according to this law: D = .128 x .15 A; where D is the 
diameter in inches, and A is the current expressed in amperes. 

The resistance of the 10-ampere arc is 74 to 4 an ohm for 
arc lengths from about ~, to an g of an inch in length. Houston 
and Kennelly give 5 ohms per inch as a rough general value. 

Carbons. — There are two classes of carbons used in arc light- 
ing, solid and cored. They may be of any diameter. For the 
sizes usually employed the average resistance is 0.15 ohms per 
foot. 

Solid carbons vary according to their purity, molecular struc- 
ture, and hardness. Coved carbons are solid except for a hole 
running axially through the carbon, filled with some material more 
soft and volatile than the remaining carbon — being usually a mix- 
ture of carbon and some metallic salt. 

Object of Core. The object of this core is first to decrease 
the voltage for a given length of arc, as already explained, or to 
increase the length for a given voltage. This has the initial effect 
of reducing any irregularity in carbons or the feeding mechanism to 
a less percentage of the whole length. Further, the core, by afford- 
ing a plentiful supply of vapor, tends to maintain a stable condi- 
tion of the arc. It also keeps the are located in one spot, and 
prevents the tendency to travel irregularly around the carbon due to 
the arc seeking the path of least resistance. When this traveling 
occurs it gives rise to an objectionable flicker, owing to the shadow 


THE ELECTRIC. ARC. 303 


of the carbons being shifted in different directions, and to the vari- 
ations of energy which occur faster than the mechanism can follow. 
A core may be employed also to modify the color of the light, as 
for instance to produce a yellowish tinge due to the well-known 
sodium flame. With these facts in mind, we can explain many 
phenomena found in arcs as used in practice. 

Carbon Consumption. — With similar carbons placed vertically 
one over the other, the relative consumption will depend on the 
amount carried off by : — 

Volatilization and electrolytic action. 

Oxidation of the air. 

Mechanical disintegration by air currents. 

When carbons of different diameters are used, their life in- 
creases roughly in proportion to their sectional area, barring the 
oxidation of the air. The latter is frequently reduced, and the 
conductivity of the carbon increased, by plating about nine-tenths 
of their cylindrical surface with a thin layer of copper, leaving the 
tip uncoated; but the primary object of the plating is to reduce 
the contact resistance of the carbon. 

Volts and Amperes. — The volts and amperes required depend 
greatly upon circumstances; but for the open arcs usually employed, 
the amperes range from six to ten, and the volts from forty-two 
to fifty-two: a common value would be 47 volts and 9.6 amperes. 
In search-light projectors much heavier currents are frequently 
employed, from 50 to 150 or 200 amperes, with voltages from 48 
to 53. With these heavy currents, the carbons become hotter, 
and are oxidized farther back from the ends, resulting in longer 
points. 

Physical Phenomena. — The positive carbon wastes away elec- 
trolytically inside of the crater, and by the action of the air outside 
of the crater, causing it to waste away about twice as rapidly as 
the negative in the open arc. The negative carbon is consumed by 
oxidation of the air alone, according as its temperature is increased 
by the carbon particles deposited on it, and by the heat reverber- 
ated from the positive crater. The closer the positive approaches 
the negative, the greater will be its roasting effect on the latter. 
With very short arcs, the deposit of graphitic carbon upon the 
negative accumulates faster than it wastes away, so that it forms a 
nib or second point on the top of the negative which finally 


304 ELECTRIC LIGHTING, 


- 


crumbles away. This action may or may not be accompanied by 
a hissing noise. 

Carbon turns to Graphite. Carbon that has been exposed to 
the heat of the arc turns to graphite. The hard pencils of solid 
carbon used for high-tension lamps will not mark paper before 
being used. After having been burned a few minutes the tip of 
the negative will write black like a pencil, and even the point 
of the positive will show some graphite. 

Electrical Relations. — With both solid and cored carbons a 
point may be reached when the voltage will be constant if the 
arc length and current are kept the same. ‘This is called the 
stationary state. In Fig. 259 the relation of the voltage to 





































































































































































































































































































pe eat fi 
H Sr itiitiiitieecitiil 
i [| | 
5b zB nae 2'364-in 
~ = ~ 1.970-in 
: os i 1.576_in 
IN _ 0:788-in! 
— 10.394-in 
Zs 0:276-in 
|_| 0.197in 
| i 4 
C1 , CI 
20 4 6 8 HP 121 14 761 iso feet re 24 26 ada 
i Coo Sige eID a SIRI RI 




















Fig. 259. Voltage and Current with Cored Carbons. 


current is plotted for several apparent arc lengths with both 
carbons cored. It will be noted that with short arcs, less than 
zs inch long, the voltage rises as the current increases, due to 
the increased CR drop. With arcs longer than , inch, on the 
other hand, the voltage falls with increasing current, due to the 
expansion of the long arc, whose larger cross-section more than 
compensates for the drop caused by increasing current. This, at 
one time, gave rise to a theory that the arc had a negative resist- 
ance, an entirely unwarranted conclusion. For arcs of 45 inch, the 
spreading action of the stream exactly counterbalances the increase 
current ; so that for this arc length the voltage remains constant 
within wide fluctuations of current. In arcs shorter than ss inch 
the stream has no room to spread laterally. Another reason for 


CHENELECTRICOARC 305 


the lower voltage with increased current shown by the curves of 
longer arcs is that the current increases while the cooling surface 
does not, so that less energy, and consequently less voltage, are 
required to maintain the arc at the same temperature. 

Effect of Cored Carbons. The same relations are shown in 
Figs. 260 and 261, except that the results are for a cored and 








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a im | | 
|7Q_Volt TH | aI [ 5 
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HERES in eee reer rte cH EH 32192 in 
— i i ‘| re CCT + | [ 
fe r mistics rales lye [| TEA | al 
2A Se cS “970 in: 
1 3 OF IN T niaintal i 
(+9 ao a ~-Hissing Arcs E82 6[ (ae 
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ri igh \ 0:788-in; 
[ a 0.394-in. 
} eat 
Beem EEE EEE - Erte 0.497-in- 
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SI 9 a Nd a ag ag a aa 
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Fig. 260. Voltage and Current with Solid and Cored Carbons. 
1185-V; 
& | a 
Ete a H ECC Eee rt u 
ie T 
80 Ty | 
} a (aa) a 
1 ct a 
75 7 
rH a 
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55 26047 Per 
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0 rp 4 10 2 14 6 181120. Pram [24 1196 28 1130 Amp. 





































































































Fig, 261. Voltage and Current with Solid Carbons. 


306 ELECTRIC LIGHTING. 


solid, and for two solid carbons respectively. The former show 
conditions approaching those found when using both carbons cored. 
But beyond a certain current strength all the arcs pass through a 
condition of unstable equilibrium, and no length can be found 
where the voltage will remain constant for all currents, plainly 
demonstrating one of the advantages of using cored carbons. 
When both carbons are solid no length of arc gives even approxi- 
mately constant voltage with varying current and a quiet arc. 
The constant voltage beyond the unstable condition is for Azssing 
arcs. With cored carbons the voltage is from 3 to 6 volts less than 
with solid carbons, owing to the greater volatility of the electrode. 

Resistance of the Arc. —If the current is kept constant the 
resistance of any arc zucreases with its /ength. With solid carbons. 
the ratio is a linear one as shown by Fig. 262, and nearly so for 
cored carbons as given in Fig. 263. | 





















































































































































































































































| 
: 4_Amp. 
18-Ohms 
16 ne 
+ oe 
| 
T ih a | 
14 eee 
at qr isle F 
cli ed ae = a ae 
12 
6. 
1-0 
L 
8 & 
EB 
5 Pu re 10 
72 
14 
4 
0-39 04788 1-182 17576 1:970 2:364 2:758-inches 














Fig. 262. Resistance for Different Arc Lengths with Solid Carbons. 


THEO ELECTRIC ARC. SOW 


As explained before, if the current is variable, the resistance of 
the arc stream proper varies inversely with the current. There- 
fore, the apparent resistance of the arc, which is the quotient of 
the volts and amperes, may be expressed by the formula, 


Aa x al, 


where x is some quantity varying inversely with the current and a@ 
is a constant. Multiplying both sides by the current / we have 


10k a (PA AUE 


IR = E and x/ is composed of a term varying inversely with the 
current and one directly proportional to it, so that we may sub- 













































































































































































































































































































































































+ r 
20-Ohms 
7-8 
ahaa 
4 4-Amp 
16 i 
14. 
T = i! 
—- 3} 
— 
7-2 
| 
| 
| | 
1-0 
Aa, i) 
7; 
H 1 mI ara 
-8: 
: 1 
mee 
mt a) 
6. | 0 : 
15. 
20 
2. Pe, 
tls 
| | 
(4) 0.394 0-788 17182 TA ae 2.364 27758 37152-inches 



































Fig. 263. Resistance for Different Arc Lengths with Cored Carbons. 


308 ELECTRICMLICHA NG 


stitute a constant # for it. We may also substitute a value x 
for the product a/, so that the voltage E at the arc is 


E=m-+ uni. 


The most probable values of these quantities for good solid carbons 
seem to be those obtained by Duncan and Rowland for good pure 
carbons, namely, # = 40.6 and x = 40, where 7 is the length of 
the arc expressed in inches. 

Watts at Arc.—If the current is kept constant the watts 
increase in a linear ratio with increase of arc length as shown by 
Fig. 264. If the arc length is constant and the current increases, 
the watts will vary in a similar manner, as shown by Fig. 265. 

Hissing Arc. — When an arc is shortened, or its current in- 
creased until it hisses, the voltage drops 10 to 20 volts, and stays 
constant even when the current varies greatly (Figs. 260 and 261), 
for which no satisfactory explanation has been afforded. 

Photometry of the Arc. — The chief source of light in the arc 
is the intensely heated crater, which gives about 85 per cent of the 
total light. The arc proper, or flame between the electrodes, is almost 
non-luminous, giving only about 5 per cent, while the tip of the 
negative carbon gives about 10 per cent. Owing to the form and 
arrangement of the carbons, as shown in Fig. 258, most of the 
light is thrown down when the positive carbon is above, as it usually 
is. The exact distribution varies with the current, carbons, and 
other conditions ; but the general distribution of light from a con- 
tinuous current arc is shown in Fig. 266. The lengths of lines 
drawn from the arc to points on this curve represent the relative 
candle-power at different angles. It is evident from this diagram 
that it is possible to obtain various values for the candle-power of 
the arc according to how the measurement is made. As a matter 
of fact, candle-power is actually measured in four different ways : 

Candle-Powers. — 1. The mean horizontal candle-power, usu- 
ally the smallest of the four, being the average in all directions in 
a horizontal plane. 

2. The mean hemispherical candle-power, usually greater than 
the last, which is the average obtained by making measurements in 
all directions and angles below the horizontal, showing the average 
value of the illumination thrown downwards. 

3. The mean spherical candle-power, determined in a similar 


THE ELECTRIC ARC. 309 






















































































































































































































































































































































































































































































850-Watt 
&00 
| ft 
Las SSeRe8ne88 
[ as Nome aa) 
T | if Lr) | 7] i 
700 [| ys | 
1 A 
| | we, 
650 | | 135 
+ i pity 
600 ab 
eas 
t Law 
550 \\ 
iZ = NOE 
500_| Ni = 
T Too | 
LH ot 
we 
7 oh 
450 
Ht ray 
40 
“a Tarn Cl C 
1 =I a alae is 
350 
ame: a 7 bak 
6 AL = an 
300 
g AME el 
250 
a Ame 
200 
g Ame 
: | | 
150 
+—t 
Ech Asi ela 
= a a eg ee af } 
700__L0 0.3941 10.788 _|17.182(|1.576_|1.970\|_|.2.364_| 2.758 in. 
l mene & is 























Fig. 264. Power consumed for Different Arc Lengths. 


510 ELECLRLCMLIG I Lay 


way, but the mean of measurements at all angles above and below 
the horizontal. This gives the true average candle-power of the 
arc in all directions. 









































































































































































































































































































































































































































if TT | f 
900_Watt i | + 
KEEH +H ] | HH | | | | | FH 
“| 7 eae 4 eaneeee 9-75 8-hn 
800 ror 
i 1-970 .in 
7002 PEPER EEE CEE eee Ht 
| rt aha PEEEEEE EEE : Cc ht 1-182) in 
SaeeuEe ! Ht HHH F a : 
600-1 (2S SRSsooseaess Soe SSSES58 0:394-in 
4, = }— ba bet ed Lt = | Ua SS ae = Si = ge 
C1 SuGeeRauRE aa t + 
500-4 rH aan Seeeeee sa = 
saad fosidfosstosstfasrittoee seats ; 
I | | |_| bl _ 
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FEEEEH EEE td Peete H 
300 
A is 
| a +f 1] 
hehe | Bis 
FLEE reo 
1001 H 
1 
4 i z + + 4 Seceeee 
PEATE ere te ae ee oe Coe og er 19 oy 814 Am, 


































































































Fig. 265. Power consumed for Different Current Strengths, 





180 170 160 150 140 


Fig. 266. Light Distribution, Direct Current Open Are. 


4, The maximum candle-power found by making observations 
in all directions to ascertain the greatest candle-power. This is 
usually found at an angle of 40 degrees below the horizontal. 


THE ELECTRIC ARC. SLL 


5] 


The term “ zominal candle-power” is often employed in com- 
mercial work, meaning a value arbitrarily agreed upon to corre- 
spond to a certain consumption of energy at the arc. Thus an arc 
consuming 450 watts is assumed to have 2,000 nominal candle- 
power, and one of 300 watts to have 1,200 candle-power ; although 
these figures greatly exceed the true spherical candle-power, they 
may come somewhere near the maximum under favorable condi- 
tions. Asa matter of fact, the relation between watts and candle- 
power is quite variable, as shown later. 

Of the various candle-powers the mean spherical candle-power 
is the most absolute and important, but unfortunately is the most 
difficult to determine. The mean hemispherical candle-power may 
be properly considered where illumination is required in one direc- 
tion only, as in street-lighting, where the light is thrown outward 
and downward. The mean horizontal candle-power is of no special 
importance, the light given off in a horizontal plane being of no 
more value than that emitted in any other direction ; but it is quite 
easily measured, and often approximates closely to the mean spher- 
ical. This is, however, not always the case, and cannot be gene- 
rally relied upon. The formula due to Gerard is sometimes 
employed to find the mean hemispherical candle-power by simply 
measuring the horizontal and maximum candle-power, the expres- 
sion being : 

Mean hemispherical candle-power = } mean horizontal + + max- 
imum. This gives only approximate results, but can be used to 
save the trouble of making a large number of photometric deter- 
minations. ee 

Relation of Light to Current. — Investigating the factors influ- 
encing the amount of light given off by the arc, Violle found that 
the quantity emitted by a unit surface of the crater was the same, 
whether the arc current be 10 of 1,000 amperes. ‘This was to 
have been expected, since the crater cannot be heated beyond its 
point of volatilization and still remain in the solid state. The light 
is therefore roughly proportional to the area of the crater. The 
spherical candle-power is also approximately proportional to the 
total number of watts utilized in the arc, but is of course affected 
by anything that varies the efficiency. 

Efficiency. — By the efficiency of the arc is meant the ratio of 
the luminous flux to the total heat and light radiation. Anything 


ry ELECTRICVLIGHIING. 


that tends to dissipate the energy at any place other than the 
crater of the positive carbon diminishes the efficiency. 

The arc is the most efficient source of illumination known. 
The most generally accepted value for its efficiency is 18 per cent. 
The corresponding figures for the other sources of light, are for the 
candle 1} per cent, the gas-flame 1 per cent, the Welsbach light 

4 per cent, and the magnesium light 12 per cent. 

The efficiency of the incandescent electric light is about 5 
per cent. These values are comparative but probably too high. 
Among the causes that modify the efficiency of the arc are these: 

1. The structure, density, and composition of the carbons. 
These affect both the volatilization point, and hence the tempera- 
ture, as well as the thermal conductivity upon which depends the 
amount of heat conducted away by the carbons, which is lost 
energy. Purity, softness, and evenness are desirable. 

2. ‘The cross-section of the carbons. Large carbons conduct 
and radiate more heat than small ones for equal currents, hence for 
a given current the efficiency diminishes about inversely as the 
diameter of the carbon increases. 

3. The existence of a soft core reduces the temperature of the 
crater, and tends to lower the efficiency. 

Current and Voltage. — The division of the watts at the arc 
into current and voltage is extremely important, depending on 
various factors not yet understood. Carhart found that with 450 
watts at the arc, made up of 10 amperes and 40 volts, he got a 
maximum candle-power of 450; while with the same number of 
watts in 8.4 amperes and 54 volts he obtained 900 maximum candle- 
power, just twice as much. Blondel, however, finds the luminous 
flux greatest usually below 45 volts. The discrepancies are prob- 
ably due to differences in size and quality of carbons, because there 
is naturally a certain current density for each carbon, which gives 
the best results. 

Commercial Values of Voltage and Current.— The value of 
45 to 47 volts at the arc, reached after years of commercial expe- 
rience, is probably the best. At this point the efficiency is high, 
and the conditions are about half-way between hissing and the 
flaming points. At this voltage, too, as the curves show, the 
voltage at the arc is only slightly affected by fluctuations in the 
current strength. Ordinary current values range from 6.5 to 10 


RYE ME LEGCTRICVARC. 313 


amperes for long arcs in air. Greater voltage is inadvisable, as 
it reduces the number of arcs that can be placed in one series, in- 
creases carbon consumption, tends to produce flaming, and intro- 
duces too much energy in a single-light unit. 

Less current than 6.5 amperes gives too little light for a unit, 
used under conditions suitable for a series circuit. On constant 
potential systems small open arcs of low current have been at- 
tempted, but without much success. The low current arc has a 
large cooling surface for the energy used. If for some of the rea- 
sons given later in detail, the current in the arc falls, the propor- 
tion of the cooling surface to thé energy is greatly increased, in 
fact to such an extent that the arc flickers violently or is put out 
by the chilling effect. Where arcs are inclosed in heat-retaining 
bulbs, the current may be greatly reduced before this effect takes 
place. 

Composition of Light. — The composition of the light of the 
arc has been determined by Meyer to be as follows, where the 
intensity of the yellow light is expressed by unity. Red and 
orange 2.09, yellow 1.00, green 0.99, blue 0.87, indigo 1.03, and 
violet 1.21. Taking the intensity of red as 100, Abney gives for 
direct sunlight ; Red 100, green 193, violet 228; while for arc 
light his figures are: Red 100, green 203, and violet 250. For 
eas-lisht he found the values.to be: Red 109, green 95, and 
violet 27. 

The composition of the light of the arc may be, however, 
greatly changed by the hardness of the carbon, the material of the 
core, and by the current and voltage. Hardness usually deter- 
mines the maximum temperature of the crater, while the current 
and voltage alter the proportions of the light fluxes coming from 
the yellow crater and from the violet arc stream. The vapor of 
the core acts to color the light as well as to determine the volatil- 
ization point of the crater. 

The color of the arc light approaches very nearly to sunlight, 
and it has the remarkable quality of producing a similar sunburn. 
Great caution is necessary on this account in avoiding exposure of 
the eyes to the arc at close range, otherwise a painful sunburn of 
the eye, producing a tedious inflammation, is apt to result. This 
can be avoided only by protecting the eyes oz all s¢des with leather 
goggles fitted with smoked glasses. 


314 ELE CTRICALIGH ANG: 


Short Arcs. —In the earlier days of are lighting, so-called 
“short”? arcs were employed, taking 18 or 20 amperes at about 
25 volts with an apparent arc length of ;4 to 3; of an inch. The 
object of such a short arc was to increase the number of arcs that 
could be operated in series by a given voltage. Owing to the large 
current, the carbon consumption was high and the line drop ex- 
cessive, so that these causes, combined with the frying sound and 
delicacy of regulation required, have brought about their abandon- 
ment. The long arc now employed in open arc lamps _ has 
roughly half the current and double the voltage. The carbon 
carried off the positive by electrolytic action is of course only half 
as great ; but the longer arc affords more opportunity for the air 
to oxidize the carbon, so that the carbon life in the long arc is not 
proportionately increased, ‘ 

Unstable Arcs. — Between the condition of a short arc and a 
long arc there lies a zone of instability for which the probable 
analogy is the concussive boiling of water on the dividing line 
between the stage of rapid evaporation and quiet ebullition. After 
the long arc is reached, it is necessary, in order to maintain a 
fixed voltage at the arc, to increase the distance between the 
electrodes as the current increases. The difference in the relative 
life of the carbons in the long arc and in the short arc is quite 
marked. In the short arc the positive wastes away rapidly owing 
to the heavy current, while the deposition of carbon on the nega- 
tive is almost sufficient to prevent waste; besides which the air 
currents have not sufficient room to form in the short arc. 

Blowing Out of the Arc.— A peculiar feature of all arcs is their 
liability to be blown by a strong gust of air unless fed by a con- 
stant current machine which cannot fail to maintain the current. 
A magnet will also blow out an arc if the pole is brought 
sufficiently close. This magnetic action, as previously stated, 
causes the bow shape characteristic of the arc, and in the case of 
an alternating current causes the arc stream to rapidly bend from 
side to side across the earth’s line of force. The blowing-out 
tendency of the magnet is frequently employed to direct the arc 
upon metals for the purpose of melting or heating them, as well as 
in various magnetic blow-out devices, in which the blowing-out 
effect rapidly extinguishes an arc formed between two contacts 
liable to be melted by the continued action of the current. 


THEGELEGCTRIC ARG 315 


Arc on Constant Potential Circuits. — When arcs can be run in 
series on circuits furnished by constant current machines they have 
the great advantage of having the current maintained as long as 
the arc is not cut out of the circuit, so that irregularities in the 
arc or mechanism produce only a variation in the intensity of the 
light, but the illumination, good or bad, is always maintained. 

It is, however, often desirable to run arc lamps on constant 
potential mains at the usual 110 or 220 volts pressure, where the 
current is no longer constant unless a device is introduced to make 
it so. Every constant potential arc lamp has a mechanism of this 
kind contained in the case whose function is to separate the 
carbons when the current is too high, and bring them together 
when it is too low. If well made and adjusted, such a regulator 
may respond to current variations of five per cent either side of 
the value at which it is set, which might be expected to maintain 
a practically constant current. Such, however, is not the case. 
An arc whose carbons are fed by a mechanism of this kind, zf 
connected directly to a constant potential main, will behave in the 
most erratic manner, even if it be started by hand regulation, and 
allowed to warm up before the test. The mechanism adjusted to 
respond to five per cent curregt variation now utterly fails to keep 
the current anywhere nearly constant, and the arc is very unsteady. 
This is true even if the voltage of the mains corresponds to the 
voltage desired at the arc. 

The reason for it lies in the fact, shown by previous curves, that 
the resistance of an arc decreases as the current increases, ‘which 
results in a tendency for the current to become almost infinite if 
constant potential is maintained across its terminals. Similarly, if 
the current begins to decrease, and so lessen the cross-section of 
the arc, the resistance rises and further chokes off the current, 
until the arc goes out. The arc when directly connected to con- 
stant potential mains is therefore in a state of unstable equilibrium, 
in which the current tends to drop to zero or surge toward infin- 
ity. This action, depending as it does only on the instantaneous 
cross-section of carbon vapor at any moment, is itself instan- 
taneous. The mere inertia of a mechanism retards it so much that 
the arc is out before the regulator has perceptibly moved. The 
means used to counteract the instability of the arc must operate 
as fast as the current change can take place. Such an auxiliary 


316 BLECTRIGGLIGIZ LANG. 


regulator, although an inefficient one, is made by the simple 
expedient of inserting a series resistance between either side of 
the arc and the mains. | 

The mechanism keeps the average current constant by zzcreasing 
or decreasing the length of the arc. The resistance overcomes the 
tendency toward rapid fluctuation by automatically and instan- 
taneously rvazsing or lowering the voltage across the arc gaps as 
required. As an illustration, assume an arc to be’ connected 
to constant potential mains of 40 volts, and the regulating 
magnet to be wound to pass 10 amperes with a normal length 
of are. If for-some redson’ the *currentssuddenly wdrops ito 
8 amperes the resistance of the arc rises, though its length may 
not have changed, and it requires more than 40 volts to bring the 
current back to 10 amperes and maintain it, therefore the arc goes 
out. If now we connect the same lamp in series with a one-ohm 
resistance to a 00-volt circuit, the current again 10 amperes, the 
lamp will have 40 volts at the terminals as before. Now let the 
current fall to 8 amperes. The drop through the resistance is 
only 8 volts, and we have 50 — 8 = 42 volts at the arc, which is 
sufficient to force more than 8 amperes through it, and so restore 
the current to-the normal 10-ampere value. The resistance in 
series is sufficient when the rise of voltage at the arc, caused by 
less drop in the resistance, suffices to force the original current 
through it, in spite of its diminished cross-section. If too little 
resistance is used, a given decrease of current will not produce 
sufficient rise of voltage at the arc to maintain it, and it goes out. 
If too much resistance is employed, the rise of voltage at the arc 
is excessive for changes of current too small to move the mecha- 
nism, and the lamp tends to allow the current to surge beyond its 
proper limits. This regulating or steadying action of resistance 
is of course instantaneous, as it depends on electrical changes 
and not.on inertia or mechanical motion. To a certain extent self- 
induction may have a similar tendency to raise the voltage at the 
point of rupture or increase of resistance in an electric circuit. 

‘No Resistance in Series with Series Lamps. Om series- or 
high-tension circuits resistance is not required, because the current 
is maintained, whatever the changes in the arc, by the inherent 
regulation of the dynamo. It is impossible, therefore, for the cur- 
rent to fail while the machine is in operation. 


THRGELECTRICVUARC Ben 


“ 


Constant Potential Lamps, Two in Series. The usual voltage 
of constant potential circuits being double that required for one 
open arc lamp with its resistance, being 110 volts or thereabouts, 
open arcs on these circuits are commonly connected two in series. 
If only one lamp is used, and the remaining excess of 60 or 70 
volts taken up by resistance, the regulating action of the latter 
tends to make the light vary up and down slowly, as explained 
above. On circuits with a higher voltage than 110, more lamps. 
are run in series, as for instance, 10 lamps ina string across a 500- 
volt circuit. From what has been said, it will be evident that both 
current and voltage vary somewhat in the arc on constant poten- 
tial or incandescent circuits, while voltage alone varies on a good 
series circuit. A carbon that will tend to produce a steady light, 
such as a cored carbon, is, therefore, advisable for constant poten- 
tial lamps. Again, these lamps are commonly used for interior 
illumination, so that a better grade of carbon and one that pro- 
duces a softer yellowish light is desirable. 

Troubles in the Arc Proper. — The chief troubles found in 
direct current arcs not caused by the mechanism are these : — 

Flaming, from too long an arc, or impure carbons, or half-baked 
carbons containing unexpelled gases. The flame usually runs up 
the side of the positive, accompanied by a drop in resistance and 
loss of light. 

Hissing, due to too short an arc or too vigorous vaporization or 
too coarse-grained carbons. ‘This is attended with loss of light, 
low resistance, and an objectionable hissing noise. 

Sputtering, from impurities in the carbon, or loose-grained 
carbons. 

Whistling, occasioned, as in a Chicago installation, by electro- 
static induction between the underground conductors and _ their 
metal sheaths. These current vibrations reproduce themselves 
in variations in the volume of the arc stream, producing a 
shrill noise. 

Traveling of the arc around the carbons producing unequal 
illumination and flicker. This arises from the tendency of the 
arc to continually seek the path of least resistance, which wan- 
dering increases with the area of the carbon over which the arc 
may travel, in other words, the area of the end. This may be 
remedied by the use of smaller carbons or of cored carbons, in 


318 ELECTRIC LIGHTING. 
a» 
which latter case the soft core vaporizes first, and the arc is con- 


fined to the inner surface of the crater thus produced. 

Bucking of arcs connected in series, owing to the mechanism of 
all the lamps endeavoring to correct a change of current due to 
the improper working of one particular lamp. This is frequently 
very marked on incandescent circuits, where only two lamps are 
in series. If one sticks, it frequently consumes all of the energy, 
leaving the other nearly dark. To overcome this, both proper 
design of the mechanism and proper adjustment are required. 

Alternating Arcs. — When arcs are fed by alternating current 
the arc is no longer a continuous flame, but is lighted and ex- 
tinguished at every reversal of the current. When these follow 
one another faster than 100 per second, corresponding to a fre- 
quency of 50 periods, the flicker is not apparent to most eyes. 
Owing to the reversal of the current each carbon acts as a positive 
at every other alternation. There is, therefore, no crater, both 
carbons remaining pointed, but the upper one wastes away 8 or 
10 per cent faster than the negative, due to receiving the ascend- 
ing heat. 

Voltage and Current. Under commercial conditions, using 
cored carbons, open alternating arcs consume about 15 amperes at 
30 to 35 volts. This would seem to be unaccountably less than 
that required for a continuous current arc using the same carbons ; 
but it must be borne in mind that an effective alternating voltage 
of 85 has a maximum potential of about 50 at the top of the wave. 

Function of Core and Object of Heavy Current. When the 
carbons are separated, it would appear that the first extinguishment 
of the arc as the current passed through zero would put out the 
light ; but a continuous path is provided for the current by the 
bridge of incandescent carbon vapor that persists until the voltage 
acquires a substantial value in an opposite direction. To obtain 
this effect the current used in alternating arcs must be larger than 
in continuous current arcs, and the carbons are always cored, to 
insure a sufficient supply of carbon vapor. 

Power Factor. If the current and £.//.F. are in phase the 
power at the arc in watts is the procuct of the volts and amperes. 
Steinmetz, however, has shown that since the apparent resistance 
varies with the current there must be a lag of current behind the 
electromotive force. Experiments show that the true power in 


THR ELEGTRICHARC. 319 


the open alternating arc is about 85 per cent of the apparent 
watts. ) ; 

Wave Form. The efficiency of the alternating arc increases 
slightly with the number of alternations, and is considerably 
affected by the form of current wave, which is largely determined 
by the shape of the wave of 4.47./.; a flat-top wave producing a 
higher efficiency than a peaked one. This is because the flat-top 
wave creates less interruption in the flow of current than the sharp 
pointed wave, the latter allowing the carbon a considerable interval 
between maximum values in which to cool off. 

flum. A peculiarity of the alternating arc is its hum, corre- 
sponding in pitch to the alternations. It arises from the expan- 
sions and contractions of the arc stream with the current, pro- 
ducing corresponding vibrations of the adjacent air. This has 
nothing to do with the hissing sound that may occur from very 
short arcs as with the continuous current. When the alternating 
arc hisses, the voltage falls, but less abruptly than with the con- 
tinuous arc, while the current lag is in- 
creased until the true watts are only 75 
per cent of the apparent watts. The 
hight emission of the alternating arc at 
any instant lags a little behind the curve 
of instantaneous value of the real watts. 






It never passes through zero, owing to 
the retention of heat by the carbons. 

Ei icteieyemew ith thesame energy 
and carbons the mean spherical candle- 


Vertical Axis of Carbons 


power of the alternating open arc is about 
one-half that of the continuous current 
open arc. 

_ Dustribution. The distribution of 
light is nearly equal above and below 
the» horizontaleas shown by Pig. <26%) . p50 325 


Therefore the light going upward, which Fig. 267. Light Distribution, Alter- 
nating Current Open Are. 


160 


is nearly one-half, would be wasted were 
it not for the white reflector usually employed immediately above 
the arc to throw the light down. 

Focussing Mechanism. The more equal consumption of upper 
and lower carbons in alternating lamps necessitates a mechanism 


pal) ELECTRIC LIGHTING. 


that will feed both carbons in order to retain the arc in the same 
place. See Fig. 268. Such lamps are usually connected to the 
secondary of a_ trans- 
former through an induc- 
tive resistance, known as 
an auto-transformer Or 
economy coil (see Fig. 
269), or they may be 
connected directly to a 
transformer wound to 
deliver a constant cur- 
rent (p. 171). The pos- 
sibility of substituting an 





Fig. 268. Focussing. Fig. 269. Connections of Economy - : : 
Mechanism. Coil. economy coil in which 


little energy is lost for 
the wasteful resistance used on constant potential direct current 
systems, compensates in a large measure for the low efficiency of 
the alternating arc. 

Inclosed Arcs. — The rapid consumption of the carbons in the 
open arc led many experimenters to attempt to devise methods 
for reducing it. The earlier workers devoted themselves to mak- 
ing a compromise between the arc and the glow lamp, the general 
features of which were a minute arc formed at the point of imper- © 
fect contact between two carbons. ‘These incandescent arcs were 
never successful for reasons now well understood. 

About 1882, and in the years following, attempts were made 
to inclose the arc of the constant current lamps in air-tight globes 
of various sizes, but without success. In 1894 commercial lamps 
were successfully used, in which the are was inclosed in a small 
globe or bulb of refractory glass protected by a larger outer one. 
It was found that the previous attempts to apply the inclosure to. 
existing high-tension lamps with high current and low arc voltage 
was a step in the wrong direction, but that the inclosed arc was 
well suited to low current and high voltage arcs, which would be 
desirable on constant potential systems. 

Inner Globe. ‘The inclosing bulb is an egg-shaped globe about 
5$ inches long and 23 inches in diameter, tightly sealed below, and 
partially closed above. When an arc is sprung between the car- 
bons inclosed in this manner, at first the same conditions exist as in 


THE tELEGERIGCARC. punk 


open arcs. The oxygen in the bulb is, however, rapidly consumed 
by combination with the carbon, and in six to ten minutes the bulb 
is filled with highly heated CO and CO,. These gases would soon 
-be replaced by air were it not for the arrangement of the cover of 
the bulb, which is usually ground to fit at the edges, with an 
opening in the center slightly larger than the carbon. This narrow 
annular opening, especially when corrugated internally, affords, by 
creating eddy currents of gases, great frictional resistance to the 
passage of the air, so that very little enters. The conversion of 
the air of the bulb into inert CO and CO, soon shortens the first 
long arc with 80 volts across to about 33, of an inch. The com- 
bustion of the carbons by the oxygen of the air is now greatly re- 
duced, so that the positive burns flat-ended, its loss being chiefly 
electrolytic. The positive is apt to have a slight tendency to 
become concave, while the negative tends to become convex, but 
both remaining approximately flat ended. Were it not for the air 
that seeps into the bulb the negative would not be destroyed at all, 
because not only is it not consumed, but it receives a deposit of 
carbon from the positive. It is found advisable, however, to admit 
just enough air to combine with the carbon vapor set free and burn 
it, to prevent it depositing as a black condensation on the bulb, or 
as a fragile nib on the negative. If pointed carbons are used in a 
bulb, they will become flattened after burning a short time. 

Volts, Amperes and Watts. Yhe usual energy at the arc in 
direct current inclosed arcs is about 400 watts (5 amperes at 80 
volts). It is found that when less than 78 volts is used the car- 
bon does not traverse a long enough arc to have its combustion 
completed, and with 50 to 60 volts, a deposit of this unconsumed 
carbon tends to form on the bulb, cutting off the light. When 
more than 80 volts is used, the carbon consumption is too high, 
the violet light from the arc becomes too prominent, and the arc 
has not sufficient resistance interposed in circuit with the usual 
110 volts to keep it steady. The voltage between the electrodes 
being therefore fixed at 80, 5 amperes give the energy usually 
taken in lamps on these circuits. The inclosed arc has properties 
similar to the arc in air, the difference of potential increasing with 
the distance apart of the electrodes. 

Hissing occurs for the same. reason, but flaming is less, and the 
zone of flame is absent because there is no oxygen to support it. 


322 ELECTRIC LIGHTING. 


Efficiency. ‘The efficiency of the inclosed arc is not as high as 
that of the open arc owing to the fact that more energy is expended 
in the arc stream and less in the crater, and that the flat-ended 
carbons rapidly conduct away the heat, and that some 10 per cent 
of the light is lost in penetrating the bulb. The retention of the 
heat by the bulb, however, adds to the efficiency, so that the net 
difference in efficiency is probably not great. 

Size of Bulb. Evidently a large bulb will be less efficient than 
a small one, and will also tend to produce a carbon deposit by 
chilling the vapor on its cooler surface. The size of the bulb 
affects the interval of unsteadiness which ensues when a lamp is 
started. The bulb being filled with air, which has diffused in since 
the lamp was last extinguished, the carbons are practically burning 
in the open air until the oxygen in the bulb is consumed. They 
therefore drawa long arc. After some time, depending on the 
amount of oxygen in the bulb, and on the tightness of the in- 
closure, the arc becomes unsteady; apparently because it is im- 
mersed alternately in atmospheres of carbonic oxides and oxygen, 
which greatly affects the arc’s resistance. At such times the arc 
may be so unsteady as cut itself out. Wa§th small bulbs the change 
from the open arc to the closed arc conditions usually occurs in 
from three to five minutes, after which the light is steady. Gen- 
erally speaking, the larger the bulb the longer the time before the 
arc passes through the period of unsteadiness. 

Carbons. — The carbons employed in inclosed arcs must be 
straight and smooth, otherwise they will not pass freely through 
the opening in the gas cap. This precludes the use of molded 
carbons, which have an irregular seam running the whole length, 
and requires forced carbons, the difference being considered more 
fully in the beginning of the next chapter. The carbons must con- 
tain the minimum amount of impurity, as it is all deposited on the 
inside of the bulb, hence cored carbons are not suitable. Uniform- 
ity in diameter is essential. 

The consumption of carbon in an inclosed arc is different in 
various positions in the bulb, chiefly owing to being more or less 
exposed to air currents. The greatest consumption is usually 
found to exist near the bottom of a bulb, and the smallest some- 
where in the upper portion. 

The ratio of the consumption of the upper to that of the Jower 


THE ELECTRIC ARC. 323 


varies curiously in different portions of the bulb and in different 
lamps, usually between 15 to 1 and 2 to 1. If the inclosure were 
perfectly air-tight, the negative would hardly be consumed at all, 
or might even grow larger, whereas the positive would be con- 
sumed electrolytically nearly as fast as usual. The ratio might 
easily be 100 to 1 or 1,000 to 1 in such a case. Where, however, 
the air has free access to the arc, the consumption by the air may 
be as large as by the current, and we should then have a ratio of 
about 2 to 1 for positive and negative carbons respectively. 
Rupturing the Arc. Inclosed arcs have a peculiar tendency 
to “cut out,” or break the arc, which is not found in open arcs. 
This 1s apt to occur when a gust of fresh air enters the bulb and 
strikes the arc, cooling it and instantly changing its resistance. 
_ The arc has a tendency to travel around the large flat ends of 
the carbons, which produces the effect of a flicker, owing to the 
shifting shadow of the negative. This is less noticeable in open 
arcs whose pointed carbons center the arc. Inclosed arcs will 
also operate with much higher voltage than 80 across the arc, 
provided that approximately the same percentage of drop is re- 
tained in series with it. Thus 150-volt arcs on 220-volt circuit 
taking 23 amperes are often used, but give a more violet light. 
Series Inclosed Arcs. — Considerable difficulty was first expe- 
rienced in applying inclosed arcs to series high-tension circuits. 
On such circuits the current is often already fixed by the winding 
of the existing dynamos, the majority of which are wound for 6.8 
or 9.6 amperes. If inclosed arcs, taking not less than 70 volts, 
were substituted for open arcs, taking 47 volts, the central station 
would have the number of lights on the circuits greatly reduced 
without a corresponding increase in revenue. Another objection 
is the heavy current, which has a tendency to overheat and soften 
small bulbs. Still another disadvantage is the length of time 
required to effect the short circuiting of the lamp by an automatic 
cut out when the carbons fail to feed or are consumed. With 
open arcs, the carbons burn so rapidly that the cut-out coil shunted 
across the arc acts in a few minutes, owing to the rise of the 
voltage across the arc. If the same construction were used, it 
would require about twenty times as long to effect the same 
action in the slow burning inclosed arc, so that the high-resistance 
cut-out coil, which is made of very fine wire, is liable to be damaged 


324 ELECTRICUAIGHTING 


o 


by the prolonged passage of the current through it. But these ob- 
jections have now been overcome. ‘The demand for inclosed arcs on 
series circuits was not at first so keen as at present, owing to the 
cheap carbons used and the rough quality of the light allowable for 
exterior illumination, in which efficiency is highly desirable and 
absence of glare not so much of a consideration. 

Advantages of Constant Potential Inclosed Arcs. — The rapid 
introduction of inclosed arcs on incandescent circuits in the last 
few years is due to the many advantages which they possess com- 
pared with open arcs on the same circuits. First, perhaps, is the 
saving effected in carbons, which last from 100 to 150 hours per 
pair on the average, with proper adjustment. Ordinary open arc 
carbons last about 8 to 10 hours. In fact, inclosed arc lamps are 
usually designed so that the remnant of the positive carbon may 
be used as a negative on the next run, if cut to the proper length. 
Longer life than 100 to 120 hours is probably not desirable in 
inclosed arcs, because it is obtained at the expense of an exces- 
sive deposit on the sides of the bulb, and a sacrifice of efficiency 
and steadiness from carbons of increased diameter. 

The long life of the carbons saves not only the value of the 
carbons themselves, but the greater labor-expense of retrimming. 
The nuisance of the daily visits of a lamp-trimmer, required for 
open arcs, especially in places where dust or a ladder is objection- 
able, has had a great deal to do with the favor with which the 
inclosed arc has been received. 

The ability to light or extinguish one lamp at a time is impor- 
tant ; because it effects an economy over the system of open arcs, 
in which two in series are always thrown on or off together. 

Quality of Light. Absence of sparks is another feature secured 
by the inclosing bulb. The mechanism also admits of the utmost 
simplicity in its construction. The color of the inclosed arc, with 
proper combinations of globes, approaches very closely to daylight, 
since it is possible to cut out the undesirable parts of the spectrum 
by the use of glass of the correct shade. With clear bulb and. 
globe the light is a violet tinge, which is not as pleasant as the 
modified color. The opalescent inner bulb usually employed acts 
also to diffuse the light, so that no violently luminous spot exists, 
but the light comes from the large surface of the bulb. The effect 
of this is to prevent sharp shadows, and to allow the pupil of the 


THE ELECTRIC ARGC Sa) 


eye to open wider without the sensation of glare; thus increasing 
the apparent illumination. 

Distribution. The distribution of the light in a vertical plane 
has been investigated by Messrs. Freedman, Burroughs, and Rapa- 
port, whose results are quoted herewith. They found that the 
distribution in an inclosed arc lamp is not the same as in an open 
acc lamp poeceutie. 2 (0, The 
maximum in the former is at an 
angle of 25 degrees below the 
horizontal, instead of 40 degrees. 
The intensity, after decreasing, 
reaches another high value at 40 
degrees, but not as great as at 
25 degrees. The probable expla- 
nation of this peculiar form of 


curve is, that at 95 degrees the Fig. 270. Light Distribution, Direct Current 
Inclosed Are. 





light comes obliquely from the 

crater, but is not cut off by the negative. Descending, the nega- 
tive cuts off more light ; but the rays emanate more perpendic- 
ularly from the surface of the crater until another maximum is 
reached at 40 degrees. The reflection from the bulb, and the 
position of the arc in it, would also alter this distribution. 

Eifictency. Tables XI. and XII. (Freedman) show the effect of 
a clear and an opalescent inner globe, the same being shown graph- 
ically in Fig. 271. The same investigators measured the loss 

by opalescent outer globes, which they found varied from 35 to 50 
per cent, and which occasionally is as great as 60 per cent. They 
conclude that with currents of 5 amperes and with two clear glass 
globes of the best quality the watts per candle are about .5, with 
opalescent inner and clear outer, the watts per candle are about 
.6, and with both inner and outer opalescent globes the watts 
per candle are about .95, being mean hemispherical candle-power 
in all cases. Holophane globes, whose construction is explained 
on page 334, gave the same loss of light as clear globes. 

Whether the run is continuous or intermittent will make a 
difference in the life, although only slight. Theoretically the life 
should be less for the intermittent test that when the lamp is 
kept burning without any stops, and this is found to be the case. 
The stoppage allows fresh air to get into the bulb each time, thus 


326 PEE CTRICH CIGHIING. 


increasing the consumption. When the current is thrown off a 
lamp, it is noticed that the carbonic oxide gas ignites with the in- 
rush of air, and by a series of minute explosions causes a chatter- 
ing of the gas-cap. Sometimes it burns with a quiet blue flame 
that lasts for five or ten seconds. To find theoretically the 
amount of carbon consumed with intermittent use we can calculate 
the weight of oxygen the bulb contains when filled with fresh air, 
and from this determine the amount of carbon burned before the 





clear inner globe only 
Sapo ere opal inner globe only 
—__--—_.. Opal inner +- opal oute 





Fig. 271. Light Distribution, Inclosed Arc with different Globes. 


TABLES XI. AND XII. (FREEDMAN.) 


CLEAR INNER GLOBE. OpaL INNER GLOBE 
ANGLE FROM THE HORIZONTAL, CANDLE-POWER. CANDLE-POWER. 

PO -ADOVE wis Tees ce eee ee 89 Et eat ce hal Be 152 

10°" « Poft go ah he ee ee 82 a rs ot ee aoe ae 184 

0 ey Sree ee 7 139 hae BS ee he 347 

10; below 26s gee een 501 SR yeh he tee 455 

20 ns US gion het SEO KOU) a) erie Fart aah RO GS a? 735 

25 a hy eal, ee ee eee SO i: adie, ee tes ores. 5? 

30 ‘f A te ae eae te) 5 oe A ee ar, 985 

40 W Voc! esc ae emees Etal «Lage l eT a ee ee tk ® 
50 ct Lo he oe eee LOGO Ae Br Se he ee 969 

60 “ ee ee Oe Se 6 Ce ee ee 855 

70 a a) Wee hh SW Are See ee ee eee 734 


Mean Hemispherical. . . 8850 ON hk fede ee EU 


THE ELECTRIC ARC. ya 


admission of any more fresh air. Taking 4 hours as an average 
run, a lamp burning 140 hours would have 36 stops, equivalent in 
consumption to 5 hours run, and on this basis would consume 
carbon as if it had burned continuously for 145 hours. An air- 
tight outer globe will increase the life; but it has a tendency to 
raise the temperature of the interior sufficient to warp or interfere 
with the action of some of the parts, although it will not do so with 
proper construction. 

Alternating inclosed arcs have also reached a high state of 
perfection. In principle they are similar to the inclosed arcs for 
direct. current. The essential difference is in the use of one or - 
both cored carbons, with consequently lower voltage and greater 
current. 

With solid carbons the long arc has a tendency to be extin- 
guished, and the vapor supply of a core is required to maintain 
the conducting medium between the electrodes. Owing to the 
inclosure, which gives a stability and freedom from interference 
of air currents, it is sufficient to use one cored carbon, and it is 
of course indifferent whether this be the upper or the lower. It 
is not advisable to use two cored carbons, for reasons explained in 
connection with continuous current arcs, namely, the efficiency 
is more or less sacrificed, and the deposit in the bulb is increased. 

The length of arc is greater than in the direct current lamp, 
being about 3 of an inch. At the start the arc may be as long as 
} to 8” before the air in the bulb is consumed, or the resistance up 
to its maximum value. When hot, the usual current is 6 amperes, 
with a voltage at the arc of 70 to 75 volts. With 70 volts and 6 
amperes ina 104 volt circuit, the apparent watts at the lamp termi- 
nals are 625 and at the arc 420, the actual watts being 445 and 
390 respectively. The watts consumed in the inductive resist-. 
ance average 35 to 45. This resistance usually consists of a 
coil in series with the arc wound on a laminated iron core, and 
mounted in the trimming of the lamp. By connecting the 
terminals to different portions of this coil, the reactance may be 
greatly varied, so that the lamp is capable of a wide range of 
adjustment for various circuits. As a rule the reactive coil can 
be adjusted to maintain 75 volts at the arc for circuits varying in 
voltage from 100 to 125, and in frequency from 60 to 153 cycles 
per second. 


328 ELECTRIC! TIGHTING 


A striking advantage of the inclosed alternating arc is its free- 
dom from the hum that characterizes open alternating arcs. This 
is due to two causes. In the first place, the mere inclosure in a 
fairly well-sealed bulb reduces the noise, but the action of the bulb 
in keeping the gases hot is the more potent factor. It will be 
recalled that in the case of the open alternating arc the hum was 
produced by the rapid expansions and contractions of the arc 
stream following the waves of current. When, however, the arc is 
surrounded by a heat-retaining envelope of glass, the gases at the 
arc do not contract as violently with its instantaneous extinguish- 
ment, hence the amplitude of the vibrations, and the consequent 
hum, are much reduced. 

Another source of noise in alternating lamps was the vibration 
of the laminated iron of which all magnetic parts are constructed. 
The thin sheets alternately repelling each other, and losing the 
repulsive force, are sent into violent vibration, which readily com- 
municates itself to the whole lamp, with an effect like that of a 
sounding-board. 

Since by the modern method of inclosure the noise of the arc 
itself has been nearly eliminated, corresponding efforts have been 
made to reduce the hum of the iron. By clamping the core of the 
reactance coil and magnet cores at a great many points, the iron 
is held too firmly to vibrate. The iron parts are then supported 
entirely on springs and rubber, both in light compression, so that 
the vibrations are not communicated to the lamp frame. Tight 
inclosure of the whole lamp completes the deadening effect, so 
that modern alternating arcs are made nearly noiseless. 

The life of the alternating arc as usually constructed is much 
less than that of its continuous current congenitor. Owing to the 
complication in the mechanism caused by feeding both carbons 
simultaneously, and the difficulty of feeding through both ends of a 
bulb, the alternating inclosed lamp is usually constructed so as to 
feed only the upper one. But in an alternating lamp both carbons 
are equally consumed, and it becomes necessary either to make the 
lower carbon excessively long or to shorten the life. The latter 
is considered preferable, and the average life is about 80 hours 
with ordinary inclosure. For this an upper carbon of 9} x }, 
and a lower one of 6 x } inches are usually employed. 


ARC LAMPS. $29 


Girit A Pier Rae xo ve 
ARC LAMPS. 


Carbons. — Manufacture. The performance of the arc light 
is so largely dependent on the quality of the carbons employed 
that some knowledge of their method of manufacture is of great 
assistance. Many of the discrepancies that have been found in 
laboratory experiments and commercial work are due to the fact 
that different kinds of carbons were employed. 

Carbons are of two kinds, according to their mode of manu- 
facture, molded or forced. “The molded carbon, as its name 
implies, is shaped in a steel mold. The forced carbon is squeezed 
while plastic through a circular orifice. The preliminary stages of 
treatment being similar, a single description will suffice for both. 

Various matertals have been employed; but the most promi- 
nent is petroleum coke, which is a product obtained in the distilla- 
tion of paraffin. Other materials, such as gas-coke, lamp-black, 
are also utilized for this purpose. The material is first crushed, 
then placed in retorts heated toa high temperature for 10 to 50 
hours according to the result desired, thereby driving out moisture, 
and imparting the quality of conductivity. The carbon is next 
ground to a fine flour in mills, and then bolted. The carbon flour 
thus produced is put in mixing kettles or pans combined with the 
“binding material” consisting of pitch which has previously been 
crushed. These pans are kept warm, and the entire mixture is 
constantly stirred by hoes or other means for a period of fifteen 
minutes to an hour. The heat causes the particles of pitch to 
attach themselves to the particles of carbon. The mixture is 
then cooled, and again crushed, ground, and bolted, so that a flour 
of uniform grain is produced. 

Molded Carbons. From this point the treatment of the 
material depends upon whether. molded or forced carbons are to 
be produced. If the former, the material is brought to men 


330 ELECTRIC LIGHTING. 


working at benches, and provided with steel molds. These are 
split in halves, being grooved according to the length and diameter 
of the carbon cylinders to be made. The molder weighs the flour 
in a scale, distributes it evenly over the surface of the mold, and 
places the steel cap upon it. The mold is then slowly heated in 
an oven, which causes the particles of combined pitch and carbon 
to become pasty. When the proper degree of heat is reached, 
the mold is taken from the oven, and placed under a hydraulic 
press, the pressure employed varying between 100 and 400 tons. 
From the press the molds are taken back ‘to the benches, the 
cover and sides removed, and the “card” of carbons carefully 
lifted out. When they become cool they are separated from each 
other ; and the little “fins”’ that have held them to their neigh- 
bors are scraped off each side, so that each carbon is left a fairly 
perfect cylinder. For lamps fed by a constant direct current, car- 
bons are usually made by the molded process, to which they seem 
best adapted. 

Forced Carbons.— Arc lamps for constant potential or alter- 
nating currents require a carbon whose particles are arranged dif- 
ferently from those in the molded process, and also in many 
instances a core of less dense material to insure steadiness of 
light. The flour for carbons to be made by this process is treated 
somewhat differently from that of the molded variety. It is 
usually shaped into cylindrical “plugs” about 6 inches in length, 
and from 2 to 6 inches in diameter. ‘These are placed in front of 
the plunger of a hydraulic press whose action is horizontal, and 
are forced through its jaws, taking any desired cross-section from 
the outline of the die at the mouth. As fast as the carbons 
issue from the die, they are received upon a table, and cut to 
desired length. In order to make them “cored,” a hole about 
1 of an inch in diameter is left in the center of the carbon as it 
passes through the die, by the action of a “tongue,” projecting 
into the orifice of the die from the inside. ‘There are various 
combinations for the mixture that is used to fill the core, and the 
secret of its composition is usually guarded by manufacturers. 
This point in either process is called the “green carbon” stage. 
They appear shiny black in color, are quite heavy, break easily, 
and when held in the fingers, and tapped together, give only a 
dull sound. Both molded and forced carbons are next taken te 


ARC LAMPS. Hol 


the furnace-room where the volatile matter contained in them is 
driven off. [his is a process requiring great care. If they are 
baked too rapidly, they warp, and are hard to adjust in the 
lamps. If they are not baked sufficiently, they are too low in ~ 
conductivity, and give a very poor light. In some cases the 
baking is performed in fire-clay pots, this being the process 
employed by many foreign manufacturers. In this country it is 
customary to lay the carbons in a large rectangular furnace, layer 
upon layer, separated by beds of sand, the entire mass protected 
by a covering of sand several inches in thickness, and subjected 
to heat until every carbon has reached a high temperature. The 
total time occupied is very considerable, being often one or two 
weeks from the time the charging begins until the process is 
completed] sw lromm the {furnace the carbons, are «carried to: the 
sorting-tables, where they are tested by rolling them on steel 
plates of true surface in order to separate the straight from the 
crooked ones. Some of the latter are sold as seconds, others 
are cut into short lengths, and the worst ones are rejected. 
Even in the best imported forced carbons there are often found 
from 2 to 5 per cent of badly warped carbons. 

Molded carbons differ from forced carbons in many ways. 
They have a loose granular structure that runs lengthwise through 
the carbon, at right angles to the line of pressure. They also have 
the remnant of the web that holds a card of carbons together ; and 
even if this is ground off, the surface is not perfectly cylindrical. 
Impurities are more likely to be found in molded than in forced 
carbons, and they are not as uniform as the forced article. They 
are used in series constant current lighting chiefly, where cheapness 
is the greatest consideration. 

Copper plating these carbons is often resorted to, with the 
objects of increasing their conductivity, especially at the point of 
contact with the clamp, and prolonging their life. The copper 
sheathing protects the carbon near the arc from oxidizing so 
rapidly, and a 12” x 8” coppered carbon in a 10-ampere lamp will 
burn about 14 hours, whereas the plain carbon of the same make 
‘vill not last more than 12 hours. 

The forced carbon is usually a higher grade of carbon than the 
molded, especially those imported from Germany and Austria. 
The texture is finer, and the material softer, than in the molded 


Bog ELECTRIC LIGHTING. 


form, while the grain runs transversely or at right angles to the 
line of pressure. Owing to the method of manufacture such 
carbons are more easily made to a given diameter, and are more 
uniform in diameter, structure, and straightness than the molded 
carbon. They have a comparatively high conductivity and are not 
copper plated. They are used for cored carbons particularly. 
The high grade and pure forced carbon more nearly resembles 
lampblack, and will make a mark on paper like a pencil, whereas 
the hard forced carbons will not. Where carbons are held by a 
small clamp far from the active end, and must fit closely but freely 
into an opening little larger than the carbon itself, too much stress 
cannot be laid on the necessity of securing straightness and 
uniformity. All carbons contain impurities, chiefly silica, iron, and 
smaller quantities of other substances. In the highest grade of 
imported carbons the silica is the chief impurity, with little else, 
but chemically pure carbons have not been produced by any 
manufacturer. 

Carbons may be cut to any desired length by nicking them all 
around and breaking them as one would a glass tube. In 
inclosed arcs and in alternating arcs both carbons are the same 
size, whereas in focussing high-tension lamps and in open arc low- 
tension lamps, the upper carbon is usually about }” larger in 
diameter than the lower. The only carbons that are copper-plated 
are those used in high-tension, series, constant current lamps. 

Globes. — The glassware used to inclose the arc has received 
little scientific attention heretofore, and it is not at all unusual to 
attempt a five or even one per cent saving in generating the cur- 
rent, and allow a 30 per cent loss in its utilization to go neglected. 
Globes are made of three materials, clear glass, opal (or opaline or 
opalescent) glass, and a combination of the two called alabaster. 
Arc lamp globes are either blown or molded. If the former they 
will vary in regularity, some being thicker, more or less curved, 
etc., than others. Often the mark of the tool used by the glass- 
blower to shape the globe as he turns it will produce streaks. 
Molded globes are quite regular, but frequently show the joints 
running vertically down the side of the mold. Clear glass globes 
when clean, thin, and of good quality transmit 90 to 95 per cent 
of the light. When dusty, thick, or of poor glass the loss is easily 
doubled. The most common defects in these globes are bubbles, 


ARC LAMPS. 333 


ribs, and other inequalities which cast shadows, and render the 
illumination very uneven. 

Opal globes are made of a glass into which some substance, 
frequently iron, has been introduced, making it translucent, but 
partly destroying its transparency. This is done to diffuse the 
light, and to cut off certain undesirable colors. The globes will. 
vary from one through which outlines can be readily distinguished, 
to those whose appearance resembles a china plate. The denser 
globes effect a greater diffusion, but frequently cut off the greater 
part of the light.” A light opal globe: may cut off 20 to 35 per 
cent and a heavier one from 35 to 50 per cent. 

Alabaster globes are made of two layers of glass, one clear and 
the other translucent. They are usually very dense, and cut off 
40 to 60 per cent of the light. In order to combine the high trans- 
missive power of a clear globe with the diffusion of an opal one, it 
is customary to grind clear globes, dividing the surface into equal 
portions. The dividing line may be either vertical or horizontal. 
The former is usually employed where the light is to be thrown in 
a direction away from the spectator, as, for instance, into a show 
window from a lamp hung in front. The horizontally half-ground 
globes are often used for the illumination of large interiors where 
an intense light is to be thrown on the ceiling and upper walls for 
diffusion and a less glaring light to the floor below. The effect 
of the grinding, which is usually done by a sand-blast applied to the 
outer surface of the globe, is to diffuse the direct rays of the arc, 
and form a brilliant scintillating surface. When the roughening is 
caused by acid the effect is less marked. When applied to both 
outside and inside of a globe the diffusion approaches that of light 
opal. A very successful effect for interiors is produced by grind- 
ing the lower two-thirds of the surface of the globes, thus cutting 
off the direct arc rays, even to those standing some distance away. 

The general shape of arc lamp globes is such as to protect the 
arc from side winds, with less attention to inclosure from rain or 
snow. With open arcs the shape should be such that the globe is 
easily cleaned without removal from the lamp, not apt to crack 
from. changes in temperature, and of such curvature that dust, 
insects, etc., fall into the cup usually placed beneath. 

With inclosed arcs a shape which will not show a long, dark 
portion in the shadow of the negative carbon should be chosen. 


334 ELECTRIC LIGHTING. 


The distribution of the light as well as its intensity is greatly 
effected by the globe used, largely owing to internal reflection. 

The curves in Figs. 271 and 272 show approximately how the 
vertical distribution varies with different globes. 


oD! 334° 22% 


B3 «313 





90° 78% 67K 56% 45° 3378 


Fig. 272. Distribution of Light, D. C. Inclosed Are. 


Recently a new form of globe, the holophane (wholly lumi- 
nous), made of clear glass after the designs of Blondel and Psarov- 
daki, has come into use. This globe diffuses the light perfectly, 
so that every part of the globe sparkles equally brightly, redistrib- 
utes the light so as to throw downward many of those rays that 
would go upward or otherwise be lost, and is capable of varying 
the distribution to suit the purpose to which it is to be applied. 

The distribution of the light is effected by prisms, whose 
section is somewhat like the teeth of a circular saw, molded in 
horizontal rings on the outside of the globe. The vertical section 
of a holophane, Fig. 273, shows that each tooth differs somewhat 
from its neighbor. The prisms on the uppermost portion of the 
globe are so designed that the rays striking them will be totally 


ARC LAMPS. Oo 


reflected back through or nearly through the source of light, and 
emerge from the lower part of the globe on the opposite side. 
About 45 degrees from the top, the prisms deflect the up-going 
rays, so that they emerge horizontally and somewhat below the 
horizontal. From there down to the level of the arc the prisms. 
all refract and reflect the light down toward the floor or street.. 
Below the horizontal the function of the prismatic ribbings is to 
distribute the light so that the objects below the arc are uni- 





Fig. 273. Vertical Section of Holophane Globe. 


formly illuminated, weakening the intensely bright zone due to the 
maximum candle-power about 40 degrees below the horizontal, and 
lightening the darker circle that tends to exist immediately below 
the lamp. 

To secure still more perfect diffusion the globe is ribbed verti- 
cally inside, as shown by the horizontal section in Fig. 274. The 
effect of the diffusion is to make the outer edges of the globe, 
viewed from the side, appear as luminous as the center. 

Holophanes have the disadvantage of requiring a stationary 
source of light to work to best advantage. This calls for a 
focusing open arc, or a fairly stationary inclosed one, two inches 


“ 


336 ELECTRIC WHGATIING. 


variation in a 12-inch globe not being excessive. They have the 
disadvantages of being somewhat expensive, heavy, and harder to 
clean, but are a marked improvement over the old style in diffu- 
sion and economy of light. To show the care exercised in the 
design of the prisms, the manufacturers of holophanes in this 
country state: “The large holophanes have as many as 400 calcu- 
lated faces, each designed for a special duty. The profile of each 
one of these prisms is calculated by the laws of optics, and drawn 
on a very much enlarged scale to secure accuracy. The drawing 
is then reduced and transferred, by a photographic process, to a 





Fig. 274. Horizontal Section of Holophane Globe, 


steel plate, and the profiles cut out with the accuracy of engravers’ 
work. A tempered steel tool is then made corresponding to this 
template, accurate to the one thousandth part of an inch ; and this 
tool is used in cutting the grooves in the mold in which the glass 
is pressed, after which it is annealed.” 

The cuts 275 and 276 show the effect of clear and opal globes 
on the distribution of light. 

Lamp Mechanisms and Constructions. — The functions of an 
arc-lamp mechanism may be described as follows : — 


ARC LAMPS. aves 


1. To separate the carbons after having brought them into 
contact, if they were not together previously. 


2. Maintain the distance between the carbons such that the 
energy at the arc is constant. 


3. Feed one or both carbons together as they are consumed. 





































































































































































































Fig. 275. Illumination on Street Surface from Open Are. 


BRR Sa 00 ee SE eee 
| 
\ 


} 
| 
| 
| 
1 


So TEE PERO SBE MULTE ARES Ne 





Fig. 276. Illumination on Street Surface from Opal Globe. 


4, Leave the lamp in such condition when the current is 
turned off that it will resume operation when the current is re- 
newed. 


To these must be added another duty, dependent on the class 


338 ELECTRIGCJIIGHUING 


° 


of circuit on which the lamp operates, usually effected by the 
“cut out ” in one of the following ways : 

5. On constant current circuits, to maintain the continuity 
of the circuit through another path, if that through the carbons 
is broken by failure to feed or by reason of their having been 
used up or broken. 

On constant potential circuits to Open the circuit under the 
same conditions if the lamps run in parallel, or to substitute an 
equivalent resistance if two or more lamps run in series. 

Regulation may be by hand or automatic. Hand regulation is 
used where the operator is always present, as, for instance, with 
projection lanterns, searchlights, etc. For arcs employed for gen- 
eral illumination automatic regulation is invariably used. 

The general principle employed is the balance effected between 
the pull of a spring, gravity, or both against the pull of one or 
more solenoids or magnets. ‘The variations in mechanical details 
are endless. The balance is preserved when the arc is in its normal 
condition. The mechanism is so arranged that too great length 
of arc will weaken the solenoidal pull, and too short length increase 
it or vice versa. In lamps intended for series circuits, these func- 
tions are performed by two types of mechanisms, known as shunt 
and adzfferentzal. 

[un shunt lamps a circuit is led to the solenoid from opposite 
sides of the arc, so that the normal voltage across the coil, whose 
resistance may be 400 or 500 ohms, is 47 volts for an open arc. 

When the current is off, the carbons are held apart by the 
retractile force of a spring, gravity, etc. On turning on the cur- 
rent, a high voltage exists across the gap between the electrodes, 
and the solenoid overcomes the retractile force, feeding the 
carbons together. When the carbons touch, the voltage instantly 
drops, and the retractile force, overcoming the weakened solenoid, 
pulls the carbons apart, and springs the arc. When the voltage 
rises too high, the shunt coil again feeds the carbons enough to 
restore a balance. Two points are worthy of special attention in 
connection with shunt lamps. The first is that the carbons are 
apart at the start, introducing a very high resistance (450 ohms 
for each lamp in the series), unless there is an auxiliary cut-out 
circuit. This exceedingly high resistance introduces a difficulty 
in starting the average arc dynamo, and gives rise to potentials. 


ARC LAMPS. 339 


exceeding the line voltage, and possibly dangerous. The other 
feature is that the mechanism is entirely independent of current 
strength, and will maintain a given voltage across the arc what- 
ever the current. Therefore such lamps will operate on circuits 
of various current values without any additional adjustment. They 
have also the property of varying the energy, and therefore the 
light at the arc no more nor less than the percentage that the cur- 
rent varies from normal. On the other hand, when the current 
of a line abnormally increases, decreasing the resistance of the 
arcs, and tending to grow still larger, these lamps do not assist 
the dynamo to regain its equilibrium. This gives rise to a ten- 
dency to unstable equilibrium of the current in the line manifested 
by surging of the lamps or jumping arcs. 

The differential lamp when at rest has its carbons 27 contact. 
They are separated by the pull of a series coil opposing gravity ora 
spring which the shunt coil asszs¢s. In this, as in the shunt lamp, 
the pull of the shunt coil tends to feed the carbons together. Obvi- 
ously this lamp has a low resistance before the current is turned 
on, which is an advantage. The current passing through the 
carbons and series coil energizes the latter to pull the carbons 
apart, against the action of gravity, because the shunt coil is 
inert when the carbons are in contact with no voltage across 
them. This insures a rapid and positive opening of the arc. As 
soon as the arc is sprung, the shunt coil begins to act, but does 
not effect a balance until the series coil has pulled the arc long 
enough for the normal voltage. When the voltage rises, the shunt 
coil feeds the carbons exactly as in the shunt lamp. These lamps 
will work properly only within small limits on either side of the 
current to which they are adjusted. An increase in current will 
result in a stronger pull of the series coil, which will draw the 
carbons apart, until the increased voltage, acting through the shunt 
coil, again effects a balance ; less current will weaken the series, 
and allow the carbons to approach. Such lamps therefore increase 
the apparent resistance of the arc as the current rises, and corre- 
spondingly assist the dynamo in maintaining the current value 
constant. For a given variation in current, however, they show a 
greater variation in light, since they increase the arc voltage with 
the current, so that the watts rise faster than the current strength. 
One point in favor of the differential lamp is that the striking of 


540 ELECTRIC LICH IING 


~ 


the arc is a positive action effected by the current. Both styles 
of lamps give satisfaction, the most notable example of the shunt 
lamp being the Thomson-Rice, while the most prominent type of 
the differential is the Brush. 

In addition to the elementary features above described, shunt 
lamps usually have an auxiliary shunt winding of coarse wire that 
acts in striking the arc. If the fine-wire shunt coil only were 
employed, the retractile mechanism of the first lamp to operate on 
starting up would separate the carbons without drawing an arc, 
since only a very small current can pass through the shunt coils 
of the other lamps in the series. The carbons will tend to vibrate, 
like the hammer of an electric bell, until all the carbons are down 
together, when they can all pick up their arcs. The coarse-wire 
shunt passes sufficient current around the carbons when apart to 
maintain an arc between the carbons of any other lamp in the 
series: As. soon as the are is struck, the circuit, of the coarse 
wire shunt is opened by the armature or an auxiliary magnet 
or some such device. 

Cut-out.—In all sevzes lamps it is absolutely essential to 
insert a device by which a continuous path is provided for the 
current in case the carbons fail to feed, or if they are totally 
consumed, or when the lamp is to be rendered harmless for 
inspection. Ina circuit fed by a powerful arc machine the ten- 
dency to maintain the current is enormous; and an arc a yard 
long may be drawn at a potential of two thousand volts or more, 
unless some positive and reliable means exists for short circuiting 
it. These devices, known as cut-outs, are contacts connected to 
the poles of the lamps, and so arranged that they are brought 
together as required. Cut-outs should operate — 

When the carbons fail to feed. 

When the carbons are consumed or broken off. 

When operated by hand by the trimmer. 

The surfaces of the cut-out that make contact should be made 
of a metal not easily oxidized, such as silver, and with the sur- 
faces vertical so as not to collect dust. A common form of cut- 
out is a silver button on the armature making contact with a 
fixed button, when the armature is pulled all the way over by 
the shunt coil. This practice is not to be commended, since it 

does not operate if the armature itself should stick. A better 


ARC LAMPS. 341 


arrangement is an auxiliary cut-out in addition to the armature 
cut-out, which will operate even if the armature sticks. The dis- 
advantage of such a device is that it is liable to operate when not 
wanted, but this may be overcome by adjusting the auxiliary cut- 
out to act only at considerable increase over normal potential. 

The cut-out that comes into play when the carbons are con- 
sumed consists usually of a contact attached to the carbon rod 
or parts moving with it, making connection with another contact 
on a fixed part of the lamp. To cut out the lamp by hand, a 
lever is frequently provided that will have the same effect as the 
descent of the carbon. In any case, the effect of a series cut-out 
is to dead short circuit the lamp, making it safe to handle. 

On lamps that are run two in series on constant potential 
circuits, the cut-out must be set to introduce a resistance that will 
produce the same drop as the lamp itself, thus disturbing the 
other lamp or lamps in the same string as little as possible. 

Iuclosed arcs when run in series require a similar cut-out, but 
have none at all-when burning singly in parallel on incandescent 
circuits. In this case the arc breaks when the carbons are 
exhausted, and the lamp goes out. 

Long-range pull of magnets. It is evident that the magnets 
of all lamps must exert a pull on their armatures just sufficient to 
maintain a balance, whether the armature be close to or far from 
the pole. - Where the force to be overcome by the armature pull 
remains constant, the magnet or solenoid must be constructed so - 
as to have long range, that is, an even pull throughout the travel of 
the armature. 

Where, however, the attraction of the coil for the armature 
is very unequal through the limit of ‘motion, as it is apt to be 
unless specially provided for, the force of the armature is equal- 
‘ized over the range of the carbon motion by some mechanical 
device, called an equalizer, such as a pair of cams. 

Temperature Correction. Another essential feature of mod- 
ern lamps is an arrangement whereby the energy at the arc is 
maintained constant, independent of variations in the temperature, 
and hence current in the shunt coil. In shunt lamps this is 
usually effected by the somewhat expensive recourse to a special 
metal, with a low temperature coefficient, for the wire-of the 
shunt. In differential lamps it is usual to shunt the series coil 


S42 ELECTRIC TIGHTING: 


itself with a small piece of low coefficient , metal. When the 
shunt resistance increases through heat, weakening its current 
and pull, it would be overpowered by the series coil were it not 
for the fact that the copper series coil has also risen in tempera- 
ture, shunting more current around itself through the low coeffi- 
cient wire, and thereby weakening its own pull. By proper 
adjustment of this “temperature” shunt the lamp, whether hot 
or cold, may be made to maintain constant energy at the arc. 

Magnetic Circuits. — The magnetic circuits of the shunt and 
series coils have an important bearing on the sensitiveness of the 
lamp. If the shunt coil is wound over or under the series coil, 
but in opposition to it, so that it has no separate magnetic flux 
of its own, increase in shunt current will weaken the pull of the 
series coil by a certain number of ampere turns. When, how- 
ever, the series and shunt have separate magnetic circuits, and 
pull against each other, an increase in shunt current will draw the 
armature or core toward the shunt coil, shortening and strength- 
ening its own magnetic circuit, and lengthening and weakening 
that of the series. This strengthens the pull of the shunt, while 
it weakens that of the series; the result being that the actions 
of the two coils are stronger and more positive when each has 
its own magnetic circuit. 

The arrangement for feeding the carbons in arc lamps is 
usually of the non-focusing type when intended for service where 
the utmost simplicity of mechanism is essential. All street lamps 
were formerly non-focusing ; lately, however, the care of electrical 
apparatus has become better understood, so that focusing lamps 
are quite practicable. The focusing arc lamp has several advan- 
tages over the non-focusing type. One of these is that the 
shadows of the side rods and bottom part of the lamp stay in the 
same place, and do not increase in size, as occurs when the arc 
travels downward on the negative carbon. Another advantage is 
that the heat is generated at the same point, and the globe is not 
unevenly heated rendering it liable to crack. The focusing arc 
also permits the use of a very efficient reflector, since the reflector 
can be placed and maintained close to the arc. (See Fig. 268.) 
In continuous current lamps this is not of such great importance, 
because most of the light is thrown downward anyway, but in 
alternating lamps it is quite essential. For use with holophane 


ARC LAMPS. 343 


globes a focusing lamp is important, since the holophane is de- 
signed to diffuse and distribute the light properly when coming 
from a certain specified point, preferably an inch or two above the 
center of the globe. If this point of light should travel down- 
ward, as it does in the non-focusing lamps as the negative carbon 
is consumed, the action of the holophane would be much less reg- 
ular and satisfactory. The disadvantage of focusing lamps is the 
complication in mechanism required to feed the lower carbon, and 
the added difficulty of trimming. The lower carbon is usually 
drawn up by a chain passing around a wheel in the upper part of 
the lamp to the carbon-holder carrying the upper carbon. As the 
upper carbon descends, the lower one is drawn up, the action being 
regulated by a clutch working on some part of the wheel or chain 
mechanism. Another disadvantage of this type of lamp is the 
necessity for using carbons of different sizes. Thus a common 
combination is a 2 inch upper carbon 14 inches long, and } inch 
lower carbon 12 inches long, with a life of about twelve hours. 
If the lamps burn only seven or eight hours, as they do during a 
large part of the year, the remainder of the carbon is wasted. 
Whereas, in double carbon non-focusing lamps the same length of 
time would consume practically all of one pair of carbons. If it 
consumed more or less than an even pair of carbons, the remaining 
portion would be used to trim one side of the lamp, and a full set 
of carbons would be used in the other. Thus, no carbon is wasted, 
unless the lamps burn so long that more than one and one-half 
pairs of carbons are required ; in this case of course it would be 
necessary to fully renew both pairs. Again, carrying two sizes of 
carbons in stock is somewhat of a nuisance for arc-light stations 
and lamp-trimmers. 

Double Carbon Lamps. — Originally, in order to gain life, car- 
bons were made very long, and were therefore expensive and liable 
to break. A pair of carbons some 12 or 14 inches long, of a size 
that will give good efficiency and steadiness, such as ¥ inch, will 
not last longer than eight hours; and this was found too short for 
all-night service during the American winter. To meet this need, 
Brush invented the double-carbon lamp. In this lamp there are 
two independent sets of carbons, both fed by one mechanism. The 
Brush clutch, which is shown in Fig. 277, is the device originally 
used to feed one pair until it was consumed, and then the other. 


344 FELECTRIC{LICAH TING. 


As will be seen, it consists essentially of a clamp holding two 
washers, each one encircling one of the carbon rods. The carbon 
rod is gripped by the tilting of the washer when the clamp is 
raised, and the clamp is so shaped (one of the jaws being wider and 
one washer having a larger hole than the other) that one washer 
is tilted more than the other. This causes one washer to grip its 
rod before the other. As the clamp is raised, the rod first gripped 









Carbon Rod 





Carbon Rod 











Washer 
IN 



































Fig. 277. Original Brush Clutch. 


lifts its carbon from the negative, and the arc follows between the 
next carbon and its negative. In order to keep feeding the carbon 
last raised, and not the other one, a stop, or release, is so placed 
that on the descent of the clamp it will come in contact with the 
washer that has been most tilted, and release its grip on the rod 
before the other washer has struck the detent. When this carbon 
rod has descended its full length, the clamp in trying to feed falls 
still more, finally touching the release, allowing the second carbon 
rod to slip down and strike the arc. ‘The extreme simplicity of 
this mechanism found immediate favor, and the short carbons that 
it was enabled to use materially lessened the cost of arc lighting. 
Practically the same device is applied at present in a modified form 
in all double-carbon lamps. 

Carbon Feed. — Two methods are commonly employed to feed 
the carbons: In one, the clutch mechanism acts directly on the 
carbon, and this is termed direct or carbon feed. In the other. 
form, the carbon is gripped by a clamp attached to a long rod, 
sometimes to a chain passing over a wheel, and the feeding is done 
by the action of a clutch gripping the rod or wheel. When the 
rod is used the lamp is known asa rod lamp, or in the case of a 
chain or band as a chain or band lamp. 

Rod Feed. Taking up the rod feed first: The advantage it 


ARC LAMBS. 345 


offers is that the carbon is positively clamped in a holder making 
good contact between carbon and metal. The surface resistance 
of carbon is very high, causing a great tendency to arc unless the 
contacts are broad and substantial. The metallic rod usually has a 
smooth and polished surface on which the clutch grips, so that the 
action of the clutch is quite regular.. If, instead of a tilted ring, a 
modified form of clutch is used, having a longer gripping surface, 
such as shown in Fig. 278, being the new Brush clutch, nicks or 





Fig. 278. New Brush Clutch. 


dirt on the carbon rod will not affect the evenness of the feed. 
The weight of the metallic rod makes its descent sure, and the 
current is fed to it easily by means of contact brushes or springs 
bearing on it. The disadvantage of the rod is that it requires to 
be polished or kept bright ; that it is apt to warp by heat, or be 
bent by carelessness in handling; and that the length of the lamp 
is greatly increased since the carbon rod must be considerably 
longer than the carbon itself. The chain-and-wheel feed is a 
modified rod feed in which the clutch grips the wheel or chain 
instead of the carbon. This avoids the chance of bending the rod; 
and, as the wheel may be inclosed in the lamp, does away with the 
necessity of polishing the working surfaces that are tarnished by 
exposure to the atmosphere, as in the case of the rod. But the 
wlement of friction is introduced in all lamps having chain feed, 
which is apt to cause irregularity in a lamp after it has been in 
service some time and the parts have become oxidized. 

Direct or Carbon Feed. Passing to lamps in which the clutch 
grips the carbon directly, it will be noticed that they have the 
advantage of minimum length, since the whole lamp need be but 
very little longer than the added lengths of the carbons used. 
The difficulty with these lamps is that the carbon has little weight, 
and will not descend with a positive action unless it is weighted by 


546 ELECTRIC LIGHTING. 


some device at the top. This lengthens the lamp. Again, what 
is probably the greatest difficulty is the feeding of the current to 
the carbon. If this is accomplished by means of rings, or any 
sliding contact device, there will always be a tendency to arc if 
the parts become oxidized or covered with dust, since the contact 
between the. carbon and the ring or brush cannot be very good 
without introducing too much friction. Ifa flexible cord is used to 
convey the current to the carbon, it requires a form of carbon holder 
which will take up considerable room, and needs a guide to direct 
the upper end of the carbon ; furthermore a flexible cord is not a very 
reliable thing to employ, because continual bending of the wire and 
insulation will ultimately break the wire and fray the insulation. 

Clutches. — A clutch is a device intended to move freely over 
a surface in one direction, and grip it when the movement is 
reversed. The usual function of a clutch in an arc lamp is to grip 
the carbon or rod so that it cannot slip until the clutch has 
been opened by descending far enough to touch a release. There 
are any number of different types of clutch, but as a rule the 
simplest are the best. Clutches are frequently constructed like an 
ice-tongs, which grip when the supporting weight is on them, but 
release as soon as pressed down. (See Fig. 295.) Any cam sur- 
face will act as a clutch when the pivot around which the cam 
moves is fixed, and the object is gripped between the edge of the 
cam and another fixed surface. There is a critical angle at whicha 
clutch of this kind fails to work, varying according to the material 
of which the cam and the surface that it grips are made. A com- 
mon value for this angle would be fifteen degrees above the hori- 
zontal. A good clutch should release the 
surface that it grips with the minimum 
effort. -by the teleasexie lhe eitectsonma 
clutch sticking is to cause most of its 
weight to rest on the release, therefore 
varying the weight supported by the mag- 
net coils, and causing irregular lengths of 
arc. Ifa clutch sticks badly the arc will 
lengthen until it goes out, in the case of 
constant potential lamps. 

he srollerasclotch minh ig Meio aiseseit- 
evident in its manner of working. Such clutches as are not 





Fig. 279. Roller Clutch. 


ARC LAMES. 347 


specially shown will be found, in their many forms, on the cuts of 
lamp mechanism in this chapter. Other forms of mechanism that 
are not so much used in modern practice are the rack or escape- 
ment feed and the hot-wire mechanism. 

The name of the former is sufficiently descriptive, and all 
lamps operating on this principle give the same trouble that a 
clock would if exposed to heat, dust, and atmospheric influences. 
When in good condition these clockwork lamps give fine results, 
but quickly get out of order. 

The hot-wire lamp, shown in Fig. 280, is the other extreme, 
since it has practically no mechanism at all. One end of a wire 
made of an alloy with a high coefficient of expansion 
is fastened to the frame of the lamp. The other 
end of the wire, which usually passes several times 
up and down through the lamp, is fastened to a 
clutch, gripping the carbon. This clutch is held 
up by a spring working against the pull of the 
wire. For an inclosed arc lamp, the wire is in 
series with the arc. When the lamp is cold, the 
wire contracts, and draws the clutch and carbon 
down. When current is turned on, the wire heats 
rapidly, and expanding allows the spring to draw up 
the; carbon, -springine the;arc. If the current in- 
creases, the wire expands further, allowing the spring 
to lengthen the arc and vice versa. Despite its 
apparent simplicity and positive action, there are 
several difficulties with this type of lamp. One is 
the lack of sensitiveness in the wire ; because small 
current variations have little effect upon the tem- 
perature, and a mechanism of this kind is slow to re- 
spond, compared with a solenoid or magnet. If the 
arc is accidentally extinguished, the length of time 
required to cool the wire so that the carbons touch 
again, is considerable. Such lamps are also af- 





- Fig. 280. Jones 
fected by the surrounding temperature unless com- — ot-wire age 


pensating wires are introduced, which destroy the 

simplicity. For alternating lamps the hot wire has the great ad- 
vantage of being free from magnetic vibration. It is essentially a 
cheap and simple construction capable of greater development. 


348 ELECTRIC LIGHTING. 


Inverted Arcs. — In order to obtain diffused illumination the 
arc is sometimes inverted (Fig. 281), so that most of the light is 
thrown on the ceiling to be reflected downward. In such cases 













































































Fig. 281. Inverted Are Lamp. 





it is usual to feed the negative 
carbon as it is then the upper 
one. It may be a trifle larger 
and the positive a little smaller 
than usual, since the rising heat 
of the arc adds to the rate of 
consumption of the negative in- 
stead of the *positivew, Horea 
similar reason inverted arcs are 


_almosta third shorter fora given 


voltage than ordinary arcs, and 
the efficiency is diminished. 
This results because it requires 
more energy to maintain the 
heat sot thes crater jwhen. itis 
underneath, which is equivalent 
to a less length for the same 
energy. Ordinary lamps are 


also used, with upturned reflectors underneath. 


Lamp Mechanism. 





Fig. 282. 


The variations of open-arc mechanisms 





The Under Reflector. 


are almost endless, but with the previously explained principles 
any may be mastered with a little study. 


ARC LAMPS. 349 


In Fig. 283 we have the Thomson-Houston lamp mechanism, 
showing the electric circuits. It consists of a seesaw lever, LL, 
pivoted at QO, and provided with a 
long tail, 7, the motion of which 
is modified by an air dash-pot. 
Below is an electro-magnet, J7/, in 
the main (circuit) and above isa 
second, S, which is connected as 
apenunt. seul hespoles pieces are. of 
conoidial shape, protruding through 
apertures in the armatures, aa, and 
66, to give a longer range of pull. 
The lower and the upper arms of 
the clutch, marked’ R and £, close 
together when the tail, JZ, rises, 
gripping the carbon rod, C, and 
raising it. . The current enters the 
lamp through an insulated terminal at + P, flows first around JZ, 
and then goes to the frame of the lamp. 

Thence it divides, the main current finding its way to the 
upper carbon-holder, and so through the arc to the lower carbon- 
holder, whence it returns (by a route not shown) to the insulated 








Fig. 283. Circuits of Thomson-Houston 
Lamp. 


negative terminal, — P. 

A smaller portion of the current flows up around the shunt 
electro-magnet to — P. The arc is struck by the preponderating 
main current in // attracting the lever end of the seesaw lever, 
and raising the clutch. The feeding is accomplished by the 
increased pull of the shunt magnet if the arc tends to become 
too long owing to the carbons burning away. 

The resistance wire & from + FP to ¢ constitutes a cut-out cir- 
cuit, which is brought into operation by the augumented current in 
Son any failure of the main current. The small coil connected 
across from + / to the lamp frame is a mere adjustment to regu- 
late once for all the power of the series coil, JZ, relatively to the 
shunt coil, SS. 

Among the best-known open-arc lamps are the Brush (differ- 
ential), Fig. 284 ; Thomson-Rice (shunt), Fig. 285 ; Adams-Bagnal 
(differential-focusing), Fig. 286; Bergmann (constant potential), 
and Westinghouse (alternating); and many other successful forms. 


350 ELECTRIC LIGHTING. 


- 


Mechanism of Inclosed Arc Lamps. In inclosed arc lamps a 
simpler mechanical construction has been reached, by reason of 
the greater length of arc permissible, and the introduction of inde- 
pendent units on constant potential mains. The general construc- 
tion of d.c. and a.c. lamps is similar, the essential difference being 
the lamination of the magnetic parts of the a.c. lamps. 

In a d.c. inclosed arc, the lower carbon is usually fixed in the 
bulb, and the upper carbon slides down upon it by gravity. To 
spring a quiet arc the upper carbon must be lifted about % inch, 





Fig. 284. Brush Lamp Mechanism. 


and remain there, when the current is, say 5 amperes. The cur- 
rent should stay at 5 amperes whether the armature of the sup- 
porting magnet is near the upper or the lower part of its travel, 
and whether it carries the full weight of a new carbon or half the 
weight of one near the end of its run. The carbon must feed 
down a little each time the armature drops to the feeding-point, 
without greatly varying the current. In any case the current 
must be fed to the moving carbon by some positive device, as the 
contact resistance of carbon is high and variable. 


ARC LAMPS. Son 


Effect of Weight of Moving Parts. The weight of a carbon 
12 inches long and $ inch in diameter is 2 ounces. After a run 
about 6 inches will be left in the holder. Thus the weight of the 
moving parts has decreased by about one ounce. If originally the 
total weight of carbon, clutch, armature, etc., was 5 ounces, and 
it required a current of 5 amperes to hold them in balance, then 4 
amperes will balance the weight at the end of the run, and the 















Chimney 
Base: : 









Divided Insulation 
-Rocker | for Tension 
Frame _ # Spring 
Ae Chitch 
AdjuSe~ Tension. | 
able | Spring 
CIuUECH 2. 
a Bridge 
ee ~Contack. 
Clutch oe 
Adjusting Dust-proof 
Screw Cylinder 7 





Fig. 285. Thomson-Rice Lamp Mechanism. 


lamp gives less light. Unfortunately to this is added the effect of 
the dust which has collected in the bulb during the run. It is, 
therefore, very desirable to keep the current as nearly the same as 
possible, but this necessitates heavy moving parts like a carbon 
rod or weighted carbon-holder. With a total weight of 10 to 20 
ounces, the decrease of current with carbon consumption is usually 
too small to be objectionable. Having settled on the allowable 


302 ETE CTRICGALIGH TING: 


current variation from beginning to end of run, the next consider- 
ation is the current variation caused by the position of the 
armature. 

Effect of Position of Armature. The magnet or solenoid with 
5 amperes of current should exactly balance the weight of the 






















































































e oq sp / 
= 
TS ORO 
So 
V/ 
i 
r Cc 
disc) 
0 G0 ap 
oo 2 Be fe} 
Y 
Fig. 286, Adams-Bagnal!l Lamp. Fig. 287. Carbon-Feed, Constant Potential, 


Direct Current Lamp. 


moving parts anywhere within their limits of travel, usually 2 to 
of an inch. The best procedure to ascertain the accuracy of a 
mechanism is to disconnect the are gap, and substitute for it an 
adjustable resistance. Adjusting the current to 5 amperes, the 
armature will usually be found to travel upward when near the 


ARC LAMPS. BOS 


solenoid, but fall when some distance down. This would be a 
departure from perfect design, and should be avoided as much as 
possible. Magnetic parts can be constructed to balance at any 
part of a §” travel within one per cent of the normal current. It 
may occur that with an armature in the upper position only 41 
amperes will be required to hold it there, while at the lower limit 
of travel 5} may benecessary. Such alamp would have a variation 
of at least 14 amperes, depend- 
ing on the position of its arma- 
ture. The latter varies any- 
where from top to bottom, 
according to how delicately the 
clutch feeds the carbons and 
according to the voltage. If the 
clutch allows only a very small 
length of carbon to slip down 
when it feeds, the armature will 
tend always to hang near the. 
position of clutch release unless 
the line voltage rises accident- 
ally. 

Effect of Levers and Com- 
plications. Some lamps contain 
combinations of levers or link 
“motion by which the balance of 
the moving parts is affected. 
For instance, the carbon and 
holder may be partially counter- 
balanced by weights, or the 
clutch or solenoid may act 
through a lever or at an angle. Fig, 288. Electrical Circuits in Fig. 287. 
In such cases it is important 
to see that the introduction of the levers, etc., does not vary the 
weight upon the solenoid by reason of the leverage changing 
with the position of the armature. It is also necessary that the 
net weight, after deducting for any counter-balancing, is large com- 
pared to the weight of the carbon alone. 

Effect of Friction. In all lamps the working parts and carbons 
move with more or less friction in the guides, dashpots, gas-cap, 





Aya ELECTRICOLICHTING. 


etc. This introduces a variation in current equal to double the 
current equivalent of the friction. This may be detected as fol- 
lows: stroke the moving parts gently in a downward direction, 
and release them gradually. They will rise until the solenoid has 
overcome the weight plus the friction; then note the current, which 
may be 54 amperes. In the same manner raise the moving parts 
slightly, and allow them to descend gently, when the solenoid over- 
comes the weight minus the friction, and the current will be, say 
43 amperes. This would bea frictional variation of one-half 
ampere. 

Causes of Variation of Arc Voltage. It is, of course, under- 
stood that variations of current produce corresponding changes of 
voltage at the arc, where the arc is in series with a resistance as 
it is in constant potential direct current work. A further change 
arises from the increase of the resistances in series with the arc 
due to heat. A resistance drop of perhaps one volt occurs in the 
average carbon, possibly two volts in the magnet winding, but the 
larger part in the series resistance. When the lamp has become 
thoroughly heated, the drop may have increased nearly one volt 
in the magnet, and several volts in the resistance, unless it has 
been made of material having a low temperature coefficient. If the 
total increase in drop amounts to more than three or four volts 
it becomes quite noticeable in the arc. We must also take into 
consideration the fluctuation of line voltage superimposed on the 
resistance variation, which may be anything from two to twelve 
volts or more. If the lamp is perfectly adjusted to maintain con- 
stant current, the drop in the resistance being the same, the arc 
voltage varies exactly with the line voltage; if out of adjustment, 
the arc voltage is still more unsteady. 

Cumulative Effect of Disturbances. The several disturbing 
factors are sometimes cumulative, and tests on the same lamp at 
different hours of the day, with varying positions of the armature, 
different periods of the run, etc, often show an astonishing 
variation. 

For example, take the following data for a lamp, not worse 
than many found in everyday practice : — 


Current balancing a 12” carbon in a given position of armature . . . . 5’ amp. 
6“ “ 6” 6c “ same 9 6 “ oe eg ee a5 amp. 

(74 ° h . tb h h . . . . Tide | 
with a given carbon when mechanism is nising .... . . . 5: amp. 


ARC LAMPS. SH 


Current with a given carbon when mechanism is falling . .. .. . . 42amp. 
ue balancing a given carbon (armature up) ee Sane eel Bees TTI: 

: 4 aS = ( come OW! Meier mene mts... \./ OR aTnp, 
mesistance (magnetand sesistance wite) cold’; 377s. 7... . \Gobms. 
HOGRe se hal alert ye te Tee col OMS. 


Mains at different hours vary from 117 to 112 volts. 


With the lamp hot after the first few hours of its run, armature 
low, and being raised against friction of carbon in gas-cap, etc., the 
current and voltage will be : — 


Current = 53 amp. due to long carbon + 3 amp. due to position of arma- 


putea zai pere Cueto NCuOn, ames ka gh-8 os bes os) oa. G2 amperes 
Dropuntresistance Hot (762) 0. | aramen P- We i es 4a. D.VOS 
With mains at 112 volts, we have arc voltage (112 SOs OMe hy ie) see UO.2eey OLS 


with 6% amperes of current. 


With lamp cold, started after 140 hours previous burning, 
armature high and descending, the other extreme condition 
will be : — 


(Current = 5 amp. due to short carbon—?dueto friction . . . . . 42 amperes 
Resistance (maser anurresiatanceywite) COld * 1. i SM is 6 ohms 
Drop in resistance (6X42) . . . Pie ott) he apoyo ZO TT YOltS 
With mains at 117 volts arc voltage is (117283 ) Sue ts Awe le” iL eas Goe-NOltS 


with 43 amperes of current. 


This lamp might vary from 88} volts at 42 amperes to 68} 
volts at 6 amperes, without considering the variation introduced by 
the clutch release supporting more or less of the weight of the 
moving parts at the feeding-point. When it is remembered that 
the same lamps with the same adjustment are used in different 
parts of a building with an isolated plant, or in various parts of 
central-station territory where the extremes of voltages at different 
hours are much larger than those given above, and the lamps them- 
selves worse, it is not surprising that some lamps are unsteady, 
give irregular life, and show blackened bulbs. High arc voltage 
produces short carbon life and clean bulbs, low voltage vice versa. 
High current tends to burn the dust into the bulb, deposits uncon- 
sumed carbon on it, and may even soften it. Poor inclosure at gas- 
cap edges, center, or at the base of the bulb, reduces the life. Too 
perfect inclosure results in blackened bulbs, due to unconsumed 
carbon. Gas-caps often warp after being greatly heated, asbestos 
washers for bulbs often chip, dashpots stick, etc., so that when 
difficulty is experienced in the operation of a lamp it must be 


356 FLECTRICHMOE ENG 


patiently ferreted out, whether due to the lamp construction, the 
carelessness of the trimmer, or the fluctuations of the circuit. 
The curves below illustrate the result of weeding out difficulties in 
lamp mechanism one by one. Fig. 289 shows the lamp current, 
and Fig. 290 the line voltage of a poor lamp under unfavorable 
conditions. Fig. 291 is current for the same lamp, its faults cor- 
rected on the same circuit, the voltage card being the same as 

























LESS 
PEE PBS SSS WN 
SN 















= Direct Current 
OBSERVED AT aoe tees 
a 


Sy 














<> 
Were 
a ee mat 
ee gt 
Tt 
ae 





ey i 
tami 
ae 















=a 8 
EPL10:50 a.m. %7 — 1:05 p.m. 940=25shst 
S 60 hrs. to 85% hrs, 
6%" and 2'%5 





£7 
Ly 
rs 
alia 
oe 
fos Hu 
te, 
ee 
ae 
= 













j e\\ 
isnt 


Wie 
SSS 








ui 
S 
ii 
RU 
\\ 
‘Mi 






NY 

i 
it 
wu 
wh 
RUAN 





me 
\\\ 







LT 
HTT 
rreLet 
aan 
\\\ 






Fig. 289. Current Variations in Badly Adjusted Lamp. 


before (Fig. 290). As modified, it shows constant current under 
violently fluctuating line voltage. . 

Function of Dash-pots. Air dash-pots are used in most lamps 
to overcome the tendency of the moving parts to overshoot on 
account of their inertia. When constructed so.as not to become 
corroded, clogged with dust, nor warped by heat, they offer very 
little resistance to slow motion, but effectually check the too rapid 
or excessive motion due to inertia. 


ARC LAMPS. Bot 


Usual Current and Voltage. In incloseda arc lamps for con- 
stant potential direct current circuits, the’ arc is usually run with 
5 amperes, at about 79 volts. The voltage may be as high as 
95 volts if the mechanism is sufficiently sensitive. It-is usual to 
interpose resistance alone between the mains and the,arc, but it 
is claimed that a considerable amount of self-induction can be 
used to replace part ot the resistance. As a rule, the higher 






ry 
\ | 
oa 






i 






it 
KL 

















\\ 
ACOA 
awe Sea Ny 










dela 8 8% AH 
au 2:30 p.m. %3q — 3:30 p.m. 31 tH 
ey, 


HA 
tH KT TAU SSek | 
sh SS 











A 


ane 










ax | | 
yry 
TL 
“y 
K \S aw WY 





RSS 
ORS 
me 


i 





[Nee 
N/ 
Pa 
ie 
WA 
\\A 









Fig. 290. Variable Voltage of Supply Circuit. 


the line voltage, the higher the permissible voltage at the arc, but 
only within narrow limits. High-voltage arcs tend to waver and 
cut out. Roughly speaking, the most economical line voltage for 
d. c. constant potential inclosed lamps is about 105 volts. 

Constant Potential Alternating Inclosed Arcs. For constant 
potential alternating circuits the inclosed arc has come into exten- 
sive use, with a voltage of 70 to 73 at the arc and 6 amperes. 


358 ELECTRIGCHLIGITING. 


Such lamps (Fig. 292), are similar to direct current lamps except 
for the lamination of the magnetic parts, the use of an adjustable 
reactance coil in place of a resistance, and the cushioning or 
spring suspension of the parts that vibrate and tend to produce 
humming. The reactance coil is usually adjustable to compensate 
for secondary voltages between 100 and 120, and cycles from 60 
to 140. Since the lower carbon is consumed nearly as fast as the 














ea ea 
















an 


eueasl 7 Ear RD SQ 
pee 
a 






<2 


Direct Current 


OBSERVED AT 
aot 
AS 
s 


eS 








HH Chart ( JOCASIB 


LTS 
ou 






as 
Oe 






. — LE Se 

I, 
EEN AK? 

oe ee SE Ly 


aueN 
SES 








(SR 






f 
ay 


Fig. 291. Current in Readjusted Lamp. 


upper one, a. c., inclosed arcs are provided with long bulbs to per- 
mit of a long lower carbon being used. As already mentioned, 
one cored and one solid carbon give the highest voltage arc that 
will be stable. The upper is usually 9} inches long for a six-inch 
lower, this difference being necessary because the upper carbon 
is consumed somewhat faster, and because it must project from 
its holder down through the gas-cap far enough into the bulb so 


: ARC LAMPS. 359 


that the arc will not be sufficiently near the gas-cap to injure it. 


The life being limited by the length of the lower carbon, which, 
in turn, is limited by the length of the bulb, these lamps burn 
only 80 to 100 hours. Of 625 apparent watts a good lamp con- 





Fig. 292. Carbon-Feed, Con- Fig. 293. Electrical Circuits in Fig. 294, Carbon-Feed, Con- 
stant Potential, Alterna- Fig. 292. stant Direct Current, 
ting Current Lamp. Series Lamp. 


sumes only 430 to 450 true watts, of which 35 are lost in the 
reactance coil. 

Direct Current Inclosed Arcs for Series Circuits. Inclosed 
arcs for d. c. series circuits are either shunt or differential the 
same as open arcs. (Figs. 294, and 295.) They are used on cir- 


360 LOL LEGA Deter alee 10 : 


cuits of 5 to 6.8 amperes, with 68 to 75 volts at the arc, and 
burn from 100 to 140 hours. The differential lamps require some 
temperature correction to compensate for the decrease of current 
in the shunt winding of the magnet, as its resistance rises with 
heat. They may also be readjusted to circuits of various current 








—Shunt 
Magnet 






Starting 
Resistance 


Fig. 295. Electrical Circuits in Fig, 294, 


strengths by shunting more or less current through a small 
auxiliary resistance, and like open arcs are usually provided with 
a resistance in series with the automatic cut-out. When the cut- 
out operates, it short circuits the lamp terminals through this 
resistance, thus maintaining sufficient difference of potential: 


ARC LAMPS. 364 


across the magnets to enable the lamp to start up again if 
nothing is wrong with it. 

Inclosed Arcs for Series Alternating Ctrcutts. Many alter- 
nating stations have street-lighting circuits, most of which have 
been operated by series direct current 
machines and lamps, thus employing 
two kinds of generating machinery. 
Series circuits are particularly adapted 
to widely scattered lamps outside of the 
regular lighting service, on account of 
the low cost of the single-wire series 
line. Furthermore, it is usually desir- 
able to have the street lamps on one or 
more independent circuits, so that they 
may be lighted or extinguished from 
the station. By using the series alter- 
nating arc system this can be effected 
without separate machinery. It con- 
sists of the lamp circuit, and a device 
connected to the regular constant po- 
tential alternating mains, which will 
maintain a constant alternating current 
in the independent lines. 

One method is to use a transformer 
already described (p. 171) having ex- 
cessive magnetic leakage, whereby the 
secondary is made to deliver constant 
current. Another device is an auto- 
matically varying reactance coil con- 
nected directly to the primary mains, 
“which adjusts the amount of self-induc- 
tion in accordance with the instanta- 





Fig. 296. Carbon-Feed, Constant 
Alternating Current, Series Lamp. 


neous impedance of the series circuit in 

such degree as to maintain constant current. Such devices are 
capable of keeping the current at 6 amperes, within one-tenth 
ampere either way. Of the two, the variable self-induction has 
the advantage of low first cost and repair, small space, and greater 
simplicity. When of the proper size for the number of lamps to 
be governed, its power factor and efficiency are higher than those 


362 ELECTRICALIGHTING: 


of the transformer, and it permits of simple adjustment to greater 
current strength, if more light is demanded by the municipal 
authorities. It has the disadvantage of connecting the primary 
mains directly to an external circuit. Fig. 135 shows the internal 
arrangements of a 100-light General Electric series transformer 
which was fully described on page 172, and Fig. 298 the appear- 
ance of a Manhattan regulator. 









Series Magnet 
ee 
























Starting 


esic cance 


| 























Ik 
Me 


aa 


| 


Fig. 297. Electrical Circuits in Fig. 296. 


In the regulator a reactance coil in series with the lamps is 
balanced against a weight in such a manner that it incloses more 
or less of the central leg of a W-shaped core. When the current 
rises, the coil is magnetically drawn in by the core, thus increasing 
the self-induction, and reducing the current to normal. 

Fig. 299 shows the mechanism of a Manhattan series alter- 
nating lamp, which is of the shunt type. The cut-out includes a 
small magnet in its circuit, which holds the cut-out contact closed 
when it has once operated after the carbons are consumed. 


ARC LAMPS. 363 


The number of series a.c. lamps permissible on a circuit. with 
a regulator is approximately the line voltage divided by 80. More 
than this tends to cause simultaneous jumping of all the lamps. 
In either system the watt loss in the regulating device is only the 
iron loss and the small resistance loss, but the regulator has some- 
what less than the transformer. The shunt lamp has the same 
voltage at the arc as at the lamp terminals, while the differential 





Fig. 298. Constant Alternating Current Regulator. 


lamp has 4 or 5 volts less. The arc, in either case, runs at about 
70 volts with 64 amperes. The power factor of an entire system 
of regulator and lamps may be as high as 88 per cent. 

Light Effictency. The luminous efficiency of the series alter- 
nating lamp is considerably lower than that of a corresponding 
direct current series open arc, and half of the light would be 
directed upward were it not for the reflector, which may send 
downward again nearly 90 per cent of the up-going rays. 
Despite its lower efficiency, it gives satisfactory and high apparent 
illumination, since the pupil of the eye is not contracted by the 
lower light intensity from the large surface of bulb and reflector, 


364 ELECTRIC LIGHTING. 


nearly as much as from the small and intense crater of the open 
arc. The pavement below the lamp is more free from the vio- 
lently contrasting bands of light and shade, characteristic of the 
open arc, thus producing the appearance of more uniform bright- 
ness. For these reasons, largely, municipal authorities often prefer 
the series alternating lamp with its lower efficiency to open direct 
current lamps consuming the same energy. 




















Fig. 299. Series Alternating Current Lamp. Fig. 300. Mounting of Hood upon Pole. 


Street Arc Lamps must have additional features, such as 
hoods, pulleys, mast arms, suspension hooks. 

Hoods should be so arranged and set on the pole tops as to 
cast the minimum shadow. (See Fig. 300.) 

Where a lamp is suspended it is well to have some arrange- 
ment which cuts out the lamp when lowered to trim. 

That the lamp is held independent of lowering rope, and hence 
~ will not fall if rope should be broken, is a valuable feature of any 
arc suspension. (See Fig. 301.) These pulley suspensions hold 
the lamp when raised, and release it when about to be lowered. 


ARC LAMPS. 365 


On raising the lamp a knob is engaged by ridges on the sides of 
the pulley, and takes all strain off the rope. A pull at the rope 
guides the knob out, so that the lamp can readily be lowered. 
Mast arm and pole arrangement is shown in Fig 802. A suspen- 
sion canopy is shown in Fig. 303, and side bracket suspension in 
Fig. 304. An arc light cut-out switch is represented in Fig. 306. 





Fig. 301. Cut-out Pulley. 









































Fig. 302. Fig. 303. Hood for Suspension. 


Projection Apparatus. 





Special forms of arc lamps are used in 
electric projection lanterns, photo-engravers’ lamps, stage projectors, 
locomotive headlights, etc. The life of the carbons in such appa- 
ratus is of minor importance, and they are usually of the open-arc 
type. The carbons are generally inclined away from the object so 
that the maximum rays at an angle of about 45° (Fig. 307) from 
the axis of the positive carbon will be directed nearly horizontally 
at the point to be illuminated. Besides being tilted, the upper 


366 ELECTRIC LIGHTING. 


carbon is often set back somewhat out of line with the negative, 
which brings the crater at an angle without requiring the tilting 
of the carbons, as represented in Fig. 306. These lamps are 





Fig. 305. Series Cut-out Switch. 



























Figs. 306 and 307. .Position of Carbons in 
Projector Lamps. 


frequently made with hand or clock 
work feed, partly because of the diffi- 
culty of feeding inclined carbons by 
gravity, and because they are under 





the care of: an operator. A reflector 


é F ‘ Fig. 808. Search Lamp with 
with a polished or dead-white surface [Ror ast 


is placed dehznd the arc. 

In searchlight projectors, on the contrary, the arc is directed 
toward the reflector and away from the object to be illuminated. 
This is done in order that all the emerging rays shall be parallel, 
in which condition their intensity is theoretically the same at any 


ARC LAMPS. 367 


distance but practically not, owing to unavoidable dispersion due 
to the size of the light-emitting surface, aberration in the reflector, 
and the refraction and absorption of the atmosphere. With the 
crater turned toward the front of the search-light all of its rays 
that did not strike the reflector would be divergent instead of 
parallel. In search-lights the carbons may be either inclined or 
horizontal, in which latter case the positive is in front. The 





Fig. 309. Search Lamp. 


carbons may both be solid if of high-grade soft carbon, but 
frequently the positive is cored. To keep the arc stationary the 
carbons must either be fed at different rates of speed, or may be 
suitably proportioned, the positive being cored and larger in 
diameter than the negative. “Any variation of the arc from the 
focal position may be corrected by hand, using the colored-glass 
windows provided for that purpose. The feeding’ mechanism is 


368 ELECTRICOLIGHTING 


usually motor-actuated so as to be positive. At the sides the light 
is surrounded by a cylindrical casing, supporting at the rear a 
reflector far enough away not to be damaged by the heat of the arc. 
These reflectors, in cheap search-lights for mining and contractor’s 
work, are sometimes made of silvered copper, but are preferably of 
glass. The latter are made in two styles, aplanatic and parabolic. 
The aplanatic or Mangin mirror has two spherical but not concen- 
tric surfaces, as shown in Fig. 8308. Owing to its unequal thick- 


as 


Lom TTT —— — ne 


7; i = 
. = a * 
SSS 





Fig. 310. Search Lamp. 


ness it is somewhat more liable to crack than the parabolic. The 
latter is a truly parabolic piece of silvered glass about 4 inch to 
% inch thick throughout. The front of the search-light is closed 
by plate-glass strips (Fig. 309) instead of one piece, to avoid 
breakage by heat, and to allow easy renewal of a broken section. 
In case the light is intended to cover a preater area, that 1s “to 
diverge, a diverging front of lens strips, usually for a 20° diver- 
gence, may be swung into place instead of the plane strips, although 


ARC: LAMPS. 369 


the same effect may be produced by moving the arc out of its 
correct position. Average values for the current in search-light 
projectors of various sizes are about :— 


45 amperes for an 18-inch light 


SOY Ha ia DAN | ata ce 
Lobe gs B05 cates 
TEO Ee 5 Se, SGU ek 
200 «§ « & 4B «  « 


The commercial ratings of candle-power of search-lights are mis- 
leading. The average light intensity of the beam is multiplied by 





Fig. 871. Projection Lantern. 


its area to get the total flux. The rated candle-power is then 
obtained by dividing this figure by the area of the crater, which 
gives relatively but absurdly high values to the candle-power. 
Thus, supposing that an arc with a mean hemispherical candle- 
power of 10,000 were combined with a Mangin reflector two 
feet distant, the average illumination on the mirror would be 


10000 


(HF = 2500 candle-feet ; and if we neglect small losses, this will 


310 ELECTRIC LIGHTING. 


be the intensity of the beam. To multiply this value by the ratio 
area of beam 
area of crater 
denominator a figure much greater than 10,000, the true candle- 
power of the arc. A more rational method would be the product 
of the light intensity of the beam in candle-feet, by its area. 

The movements of the beam of light are produced indepen- 
dently of the arc mechanism, by hand or by distant motor control. 
In the latter instance the projector may be provided with a vertical 
wheel and chain actuated by a motor, which turns the barrel around 
a horizontal axis, as well as with a motor-driven revolving base, 
to swing the whole lamp in either direction. These motors may 
be operated by a distant controller, and the lamp suitably fitted 
with a two-joint receptable for the lighting cables and usually a 
five-point socket for the motor cables 





, gives for any possible values of the numerator and 


2NTERIOR WIRING. Sik 


CHAPTER XVI. 


INTERIOR WIRING. 


Tue laying of electrical wires does not appear to be as impor- 
tant from the engineering point of view as the construction of 
overhead and underground conductors ; nevertheless, an additional 
and most important consideration is involved, this being the fire 
hazard. When electric lighting was first introduced this difficulty 
was so great, being naturally magnified by prejudice against the 
new method of illumination, that insurance and municipal fire 
department authorities were often strongly opposed to the intro- 
duction of electrical conductors into buildings. But improvements 
in methods of construction have gradually reduced the risk, until 
now insurance companies and fire departments consider electric 
lighting less dangerous than any other form of artificial illumina- 
tion. This is undoubtedly a fact; but electrical wires are still 
the cause of many fires, the consequences of which are often very 
serious. Hence, it behooves those who are responsible for the 
installation of electrical apparatus and conductors inside of build- 
ings, to exercise the greatest possible care. This is the more neces- 
sary, in view of the cenditions under which electric. light wiring 
must be installed to meet the varied requirements. In a large 
class of installations no small amount of judgment, ability, and 
ingenuity is often required to overcome the difficulties met with, 
to adapt the material at hand to the purposes, or to devise new 
methods to secure unusual results. Slaughter houses, dye houses, 
chemical works, bleacheries, and breweries offer many peculiar 
difficulties to proper wiring. 

Before the actual interior wiring can be of use it must be 
connected with the service wires, and this necessitates in most 
cases that at some point the wires enter the building. In order 
that the moisture may not travel along the wires from outside to 
the interior installation, there is at the service entrance a drip loop 
outside ; and the hole through which the conductors must pass is 


SZ ELECTRIC TIGHIING. 


bushed with a drip tube, which must slant up towards tke inside. 
(See Fig. 8312.) The wire entering these tubes should have solid 
rubber insulation, at least ¢; of an 
inch thick, and covered with a sub- 





stantial braid. The space between 
the wires as they enter the building 
bn, 4g should be at least one foot, and ar- 
Sete Oe Diet rits oe ranged so that no cross connection 

can be made by water. The wires 
should never come in contact with anything but their insulators. 
Running them along the face of the building should be avoided, 
and they must be fastened to the wall near the entrance tubes by 
insulators mounted on special brackets having two coats of water- 
proof paint to prevent the absorption of moisture. 

Automatic cut-outs such as circuit breakers or fuses should be 
placed on each of all service wires as near as- possible to the point 
where they enter the building, on inside of the walls, and arranged 
to cut off the entire current from the building. The wires then 
run to the service switch, which should be capable of opening the 
circuit when carrying the entire current of the building. This is 
a knife switch, and should be installed so that the handle will be 
up when the circuit is closed, so that gravity will tend to open the 
switch, rather than accidentally to close it. | 

With alternating systems the best place for the transformer is 
on the pole away from the building. The transformer, when 
placed on the outside wall of the building, must be hung on well- 
insulated supports, the construction being as shown in Fig. 318. 
Where it is impossible to exclude it from the building, the proper 
place is a vault or room with brick walls containing nothing else 
but transformers. As a last resort it may be put in a part of the 
cellar where it is well ventilated and dry, being carefully insulated 
from the walls and the ground. 

The next piece of apparatus in the building is the switch board 
or in small installations the distributing panel board. This wili 
carry the meters, the knife switches and the fuses for the feeders. 
If electric power is to be used besides the lighting the separation 
of the two kinds of circuits should be made at this point. 

The principal methods which have been, or now are, used io 
carry the wires from the entrance devices to the ‘lamps are as 
follows : 














wv 


lh 





ill 


INTERIOR WIRING. 3190 


(1) Wires inclosed in molding. 

(2) Wires carried by wooden cleats. - (Obsolete.) 

(3) Wires carried by porcelain cleats or knobs in open work. 

(4) Wires carried by porcelain knobs and tubes concealed. 

(5) Wires concealed in plaster. (Obsolete.) 

(6) Wires concealed in tubes, interior conduits. 

(7) Wires laid on some cornice, wainscoting, or other architectu- 
ral feature adapted to the purpose. 

(8) Fished wires. (Not desirable.) 








ee 
y 

pe 7 

aed Ypp | 


WW 






PRIMARY |} 
CUT-OUT. |f 


<2 S32 








Ni 



































(FZ 
poe ee LT ] 
| pragma 
A ie 1 A Y 
: : a i k— W) : 
| TRANSFORMER. AL L 
y 
(eat Ey 
al ee Pele ripih | DETAISUF OC Yj 
\ \ eR RE \ G 
USUI at ee 
199) = ee is 
ite. | za ! rm 184, WATER LOOP, v 
WATER LOOP, 7 a i _ edb ie tes 
i ra 





3 DIA 15/6 
DETAIL OF A ech 


From Standard Wiring by 
HC. Cushing. jr; 


CONSTRUCTION WORK 
INSTALLING TRANSFORMERS 


Fig. 318. 


374 ELECERIC TAGHIING 


Three of these —i.e., the second, fifth, and eighth— are no 
longer considered good practice, in fact they are forbidden by the 
National Electric Code. In order, however, to fully appreciate 
the difficulties in this important branch of electrical engineering, it 
will be well to consider all of the above methods in the order 
given. 

Wooden Molding. — The advantages of this construction are 
simplicity, cheapness, and accessibility. It is particularly appli- 
cable to buildings in which no provision has previously been made 
for electrical conductors, the wires being laid after the building is 
completed. At first this was the general condition, and a very 
large proportion of the wiring laid during the early history of elec- 
tric lighting was installed in this way. At present the use of 
electric light is decided upon, or at least contemplated, before the 











Lh 4 LLL AL 
Miedo tii 
Yt 





Fig. 315. Two-wire Molding. 


building is erected, and the plans ‘provide specially for it. In such 
cases, particularly where expense is not a prime consideration, the 
use of the so-called “interior conduit,” laid in the walls, is the 
standard practice for low tension (below 450 volts circuit). For 
high-tension wires, the only approved plan is to carry them upon 
porcelain knobs or cleats. These two methods will be considered 
later, in their proper order. P 

Wooden molding usually has the cross-section represented in 
Fig. 815, consisting of a strip or “backing,” in which are cut 
grooves corresponding to the number of wires to be laid, only one 
conductor being placed in each groove. The backing is fastened 
to the wall by thin wire nails or brads, being made continuous as 
far as possible. Angles and branches are formed by fitting pieces 
together, as indicated in Fig. 817. The wires are then laid in 
the grooves, being also preferably continuous, although joints are 


INTERIOR WIRING. 315 


allowed, provided they are securely made mechanically by splicing 
and soldering, and provided the insulation is made equal to that of 
the rest of the wire by careful wrapping of tape. The capping is 
then put in place, and fastened by small tacks or brads. Molding 
has been used in which the grooves were formed in the capping 
without any backing. This, however, is bad practice, and should 
not be adopted even where the wires are laid against a wooden wall 
or ceiling. 

The chief disadvan- 
tages of wooden molding 
are the facts that it is 
not sufficiently impervi- Yiiyy 
ous to moisture, is liable ++ Ty tH: tiégzy 
to be crushed or punc- WY tog 
tured mechanically, and 
is combustible. These 
difficulties are overcome as far as possible by coating the molding, 
both inside and out, with water-proof paint, or by impregnating it 
with moisture repellent. It is also recommended that only hard- 
wood molding be used. But soft-wood molding is often laid be 
cause it follows the wall line better. In the standard forms, tne 
backing is at least three-eighths of an inch thick under the 
grooves, and one-half an inch between them. The capping should 








ti iffy 
GVH. Vs : 
eens 816. Three-wire Molding. 


SetmillarOnec-cix eclt incor alulinch WoL 
more, into the backing, and should lap 





over the grooves not less than one- 
eighth inch on each side. These min- 











imum dimensions are represented in 
Figs. 815 and 316, but much larger 
sizes of molding are used for heavier 





Fig. 317. Right Angle Joint in 
molding. 


wires. 

Rats gnawing through a molding 
may destroy the insulation of the wire, and bring the copper in 
contact with the wood. 

Wires for use in molding must have rubber insulation, at 
least @ of an inch thick; and as the size of the wire increases 
from No. 14 to No. 0000 the thickness of the rubber changes 
to>,2, inch. 

In molding where one of the wires must cross over, it is 


a her ELECTHICANGHIING. 


brought out through the capping and across it, so that a certain 
thickness of wood is between the two conductors. 

Wooden Cleats. — These may be looked upon as a discontinu- 
ous molding. In fact, their cross-section is practically the same. 
Their use is rarely to be tolerated at present, cheapness being their 
only recommendation. Experience has shown that it is a great 
mistake to attempt extreme economy in the laying of electrical 
conductors. The serious difficulties which arise in the shape of 
damage by fire and interruption of service are far more expensive 
in the long run than a considerable increase in first cost. 

Wooden cleats have all the disadvantages stated for wooden 
molding, and are open to two additional objections. One of these 
is the fact that the wires are left exposed fora large portion of 
their length, and are therefore liable to be injured or to form a 
short circuit or ground connection by coming in contact with each 
other or with some pipe, nail, or other conducting body. Wooden 
cleats are also likely to have small splinters projecting from them 
which cut through the insulation of the wires, and have been found 
to be a source of much trouble. 

Porcelain Knobs or Cleats. —In open work various forms of 
these devices are used. (Figs. 818 to 321.) This construction 























Figs. 3818-821. Porcelain Knobs. 


seems to be open to the same objection as the use of wooden 
cleats, the wires being entirely exposed. between the points of 
support. Nevertheless, as already stated, this construction is prac- 
tically the only one allowed for high-tension circuits (over 450 


9 


INTERIOR WIRING. ales 


volts) inside of buildings. The explanation of this apparent anom- 
aly is found in the fact that high-tension circuits are very carefully 
treated when brought within buildings. For example, the primary 
circuit of the alternating current system is rarely allowed to run 
more than a few feet after it enters a building, the potential being 
immediately transformed down to a safe value of about 100 or 200 
volts. Even in such cases the high-tension wires are only per- 
mitted in the cellar or other portion of the building not generally 
used; in fact, the transformer is usually placed outside of the 
building wherever possible. The series arc lighting circuits which 
are also high tension (2000 to 5000 volts) are most carefully laid 
when brought into buildings, the path being as short and direct as 
possible, and located where the wires are not likely to be touched 
by persons or to come in contact with anything but the insulators. 

They must be rigidly supported on glass or porcelain insula- 
tors, which raise the wire at least one inch from the surface wired 




















(Lia a 
baal wu pl Oh 
=F eon 


Figs. 322-824, Porcelain Cleats. 


over, and must be kept apart at least four inches for voltages up 
to 750 and at least eight inches for voltages over 750. 

Rigid supporting requires under ordinary conditions, where 
wiring along flat surfaces, supports at least about every four and 
one-half feet. If the wires are unusually lable to be disturbed, 
the distance between supports should be shortened. 

Such circuits are never introduced into buildings to anything 
like the same extent as low-tension wires, which run in great num- 
bers to all parts of most modern structures. The porcelain cleat 
is, moreover, free from the splinters which constitute a serious 
objection to wooden cleats. 

Glass insulators may be used instead of porcelain, but the latter 
is usually to be preferred because it is stronger, tougher, and less 
hygroscopic. The statement is often made that “any material 
which is non-conducting, incombustible and non-absorptive”’ may 
be used, for this or other similar purpose. In point of fact, porce- 


378 ELECTRIC LIGHTING. 


lain and glass are practically the only available substances which 
fulfill these requirements ; but if any other equivalent material can 
be found, its use would be permitted. 

For concealed “knob and tube”’ work: the wires are run on 
the timbers and studding by means of porcelain knobs, and the 
wires tied to them by tie wires of equal insulation to the main wire. 

The wires are carried through the beams by 
WA Ny AN i} 4 means of porcelain tubes. These tubes are 
(TAN. AAI 















set in the beams by forcing into auger-holes, 
and are kept in place by the friction and by 
: x | ? | the head formed on one end of the tube. 

hy, Inhale : (Fig. 825.) All the porcelain devices must 
Fig. 326. Porcelain Tube) een tthe wire (One Inc nek Oniatir mel ace 




















wired over, and the wires must be kept ten inches apart. They 
are preferably run on separate beams. They must be stretched so 
as to have no sag, and are to be supported every four feet, or even 
closer when necessary. This style of work is much used in coun- 
try houses, where an installation for a ten-room house costs only 
about forty dollars. 

The outlets are protected by a canvas jacket called circular 
loom, or by a curved porcelain tube, or even one of the beam tubes 
may be used for the purpose. 

Mill construction: in buildings of this character mains of No. 
8 wire or over, where not liable to be disturbed, may be separated 
4 inches, and run from timber to timber, not breaking around, and 
may be supported at each timber only, otherwise, the construction 
in Fig. 826 or the plan of running through the timbers in Fig. 327, 
which cut also shows a boring-tool for this work. Unless some 
special tool is used, the holes will not be in line, and unsightliness 
as well as waste of wire is the consequence. 

Wires in Plaster. — Another method of concealed wiring which 
at one time was considered to be an ideal one, consisted in embed- 
ding the conductors in the plastering of the walls and ceilings of 
a building. This method could be adopted either during the 
original construction of the building, or in case of repairs or re- 
plastering. It was employed in many fine structures where the 
best construction was desired, regardless of the expense; but it 
was soon found that the detrimental effect of the lime in the 
plaster upon the insulating material rapidly injured or destroyed it. 


INTERIOR WIRING. 379 


Furthermore, the changing or repairing of a wire was rendered 
very difficult, necessitating the tearing away of the plastering, the 
trouble being aggravated by the fact that the exact location of 





Fig. 326. Factory Wiring. 
the wire was hard to determine. The result is that at the present 


time the National Code distinctly states “that wires must not be 
laid [directly] in plaster, cement, or similar finish.”’ 





Fig. 827. Wiring through Timbers. 


Interior Conduits. — The most approved method of low-tension 
electrical wiring consists in providing tubes, usually laid in the 
floors, walls, or ceilings of a building while it is being erected, in 


380 ELECTRIC LIGHTING. 


the same general manner that gas-pipes are put in. The wires 
are drawn into these conduits when the building is nearly com- 
pleted. It is interesting to follow the development of this stan- 
dard form of construction. At first interior conduits consisted of 
tubes of insulating material, that is, vegetable fiber impregnated 
with resinous matter. Experience showed that this insulating 
tube was likely to be crushed or perforated by nails, either during 
the construction of a building or afterwards. Hence the next step 
was to protect the insulating tube with a thin sheathing of brass, 
giving the so-called “ brass-armored conduit.’’ Even this was not 
found to be an adequate protection against mechanical injury ; 
so that an iron or steel pipe, about equal in strength to an ordi- 
nary gas-pipe of the same diameter, was substituted for the thin 
brass sheathing, producing the well known “iron-armored con- 
duit.” The final stage of the development was reached when 
the National Electrical Code of 1897 allowed the use of plain iron. 
or steel pipes as conduits, “ provided their interior surfaces are 
smooth and free from burrs; pipe to be galvanized, or the interior 
surfaces coated or enameled, to prevent oxidation, with some 
substance which will not soften, so as to become sticky, and pre- 
vent wire from being withdrawn from the pipe.” This evolution 
clearly shows that the object of such a conduit is to facilitate the 
insertion or extraction of the conductors, to protect them from 
mechanical injury, and as far as possible from moisture. These 
tubes or conduits are to be considered merely as raceways, and 
are not to be relied upon for insulation between wire and wire 
or between the wire and the ground. On the other hand, the 
presence of a lining of insulating material is undoubtedly an 
advantage in most cases, and it would probably be worth the extra 
expense that it involves. The permission of the National Code 
to use plain iron or steel tubes in no way implies that they are 
better than insulated conduits. It simply means that the general 
use of some form of conduit is to be encouraged, and to this end 
restrictions are removed as far as possible. | 

The various styles of house conduit, such as brass-armored, 
paper-lined tube, etc., have been gradually discarded; and the 
standard conduit of the present time is either iron pipe with an 
inner insulating lining, or iron pipe with an enamel finish inside 
and out. The objection to rubber compound insulating lining is 


INTERIOR WIRING. 38 


the fact that if the pipe is subjected to any heat, owing to its 
being in a hot boiler-room or other location where there is an 
unusually high temperature, the insulation somewhat deteriorates, 
and renders it very difficult to pull out old wires and replace 
them with new ones. The enamel conduit is rapidly growing in 
favor, owing to the fact that it forms a good raceway for the 
wires, and it is not subject to the above-mentioned disadvantage 
of the insulated conduit. 

Electro-duct, Armor-duct and Loricated Pipe conduits are iron 
pipes with the inner and outer surfaces covered with enamel, 
whose service is to render the conduit rust-proof, as rust is highly 
injurious to rubber, which is: the insulation used on wiring in 
interior conduits. 

There are many conduits having an insulated lining, such as 
Armorite and [ron-armored conduit (Fig. 3828). These. insulations 
are of paper, wood- 
fiber impregnated with 









































a moisture repellent, 








or are of some bitu- 


Fig. 828. Insulated lron-armored Conduit. 


minous compound. 
There is also a form of conduit which is lined with vitrified clay pipe. 

‘¢ Fished Wiring.’’ — In order to avoid the unsightliness of ex- 
posed wiring, various methods of concealed wiring have been in 
vogue. The obvious plan of running conductors through the 
spaces in walls, floors, etc., of buildings, has been followed from 
the first. In one method of doing this, the wire is pushed or 
drawn by hooks from point to point, trusting largely to chance. 
Hence the process of introducing it is called “fishing.” This hap- 
hazard method of laying wires is not to be recommended, since 
it is evident that the wires may come in contact with nails, steam 
and gas pipes, sharp edges of beams, etc., which might cause 
serious difficulties. In some cases, however, it may be the only 
practicable way to carry a conductor from one point to another. 
In this case the attitude of insurance authorities on the matter 
may best be shown by quoting from the National Electrical Code, 
Rule 24, Cand S. “Wires must not be fished for any great dis- 
tance, and only in places where the inspector can satisfy himself 
that the rules have been complied with. When from the nature 
of the case it is impossible to place concealed wiring [in conduits 


382 ELEGTRIC WIGHT. 


or in the regular way] on non-combustible insulating supports of 
glass or porcelain, the wires, if not exposed to moisture, may be 
fished on the loop system if incased throughout in approved con- 
tinuous flexible tubing or. conduit.” The method of “fishing ” 
wires should never be attempted for high-tension conductors. 





Fig. 330, vJunction or Outlet Box for Flexible Conduit. 


This flexible conduit may bea flexible steel tubing composed 
of convex and concave steel ribbons wound in a spiral around a 
mandrel so as to interlock. Its use is permitted by the under- 
writers for either finished or new houses. ‘This tubing is not 
water-proof ; and some difficulty is experienced in getting the wire 
through it, owing to the fact that it is heavy, and sags somewhat 
between the points of support. 
The tubing is made in lengths 
of 100 feet, and is intended 
to be installed without joints 
between outlets. An outlet 
box and portions of the tube 
are shown in Fig. 330, and an 
iron clamp for turning a right 





angle in Fig. 3381. 





Circular loom, or canvas 





Fig. 831. Flexible Metallic Conduit. jacket, is a tubular woven 
fabric treated with compound, and rolled in mica dust while yet 
soft. This is sometimes used, one tube for each wire, in finished 
houses where the wires are fished. 

Wires unprotected and fished between walls are not allowed 
under any circumstances. 


Flextble Tron-armored conductors have come into the market, 


INTERIOR WIRING. 383 


and are successfully used for repair-work, and in places where 
the conductors are exposed, as in “drop cords’’ for example. 

Installation of Interior Conduit. — All conduits should be con- 
tinuous from one junction box to another, or to the fixtures, and 
the conduit tube should fit properly into all the fittings, else the 
conductors are not properly protected, and water is much more 
likely to enter the conduit. The entire conduit system of a build- 
ing should be completely installed, and the mechanical work on the 
building finished before the wires are drawn in. In the houses 
which are not fire-proof, tubing is generally supported from the un- 
derside of the floor beams, while in buildings of fire-proof construc- 
tion they run on top of floor beams and under the finished floor. 

The tubing of houses is generally put up as soon as the parti- 
tions have been erected; and when the tubing and outlet boxes 
have been placed, the lathing or plastering is proceeded with. On 
the completion of the plastering, the wire is pulled in, and switches, 
receptacles, etc., put in position. 

After all the conductors have been drawn in place, the outlets 
should be plugged up with a wood or fiber plug, made in parts to 
fit around the wire, and the outlet painted with some compound. 
The aim should be to make the whole system air-tight and mois- 
ture-proof. 

incaminaleatcsh eis) then madertto, sce that. there. are no 
grounds on the different parts of the wiring, and that the insula- 
tion resistance is sufficiently high to conform with the underwriters’ 
requirements. | 

The metal of all conduits should be effectually and perma- 
nently grounded. It is impossible to prevent the conduit from 
being partially grounded, and hence it should be purposely and 
completely connected with the earth. 

Conduit Wiring. — Standard rubber-covered wire should be 
used, because there is always the possibility of dampness getting 
into the conduit ; and the insulating lining of the conduit, if there 
is one, may be defective in places. The insulating lning of all 
conduits may be said to be defective, in that it is not continuous, 
but must be cut at each of the couplings. 

Conduit work is made a complete system by the use of outlets, 
junction boxes, and panel boxes with doors and locks, thus thor- 
oughly protecting the circuits at all places. 


384 ELECTRIC CLIGH TING. 


There are two types of outlet box. One where the box is made 
for a given position and number of outlets (Fig. 332), and the 
other where the number of outlets to the box is variable. In this 
















































































































































































Fig. 332. Outlet Box. 


latter type the sides are made in such a manner that a blow of a 
hammer will knock out a disk of metal and make an outlet. 
These are called Universal boxes. 

.—~ Control. — In connection with the systems of wiring that have 
\. been explained, there is the system of control, that is the same 
for all. } 

From the switch board, which may, according to the size and 
character of the installation, vary from a combination of marble 
panels to an asbestos-lined, hardwood box, the feeders run to the 
channels provided, and are.carried to the various parts of the build- 
ing. " As a rule one pair of feeders for each floor is sufficient. 

feeders are the conductors that carry the main currents to feed 
the branch circuits and mains. They also preserve the regulation 
by bringing various points of the installation to a certain predeter- 
mined potential. The feeders must be designed to carry any load 
that may be legitimately put upon them. A usual method of cal- 
culating their size is to assume the load to be 80% of the total 
load that can be brought on them, and then, with that current, 
design for about 2% loss of voltage. This figure can in small 
plants, due to the short length of the runs, be reduced to 1.5%. 

Each feeder will run directly to a panel board. These boards 


INTERIOR WIRING. 385 


vary from marbleized slate to asbestos-covered wood. The better 
kinds are inclosed in a panel box lined with slate, and furnished with 
a door and a lock. Double-pole “baby” knife switches and fuses 
are placed on the panel board. The space between the lining of the 
box and the panel board proper is known as the “ gutter.’”’ The con- 
duits of the various tap-circuits enter this gutter, and the wires 
are protected from the ends of the conduit by bushings. All wires 
in the gutter are inclosed in flexible tubes, and connections are made 
on the panel-boards by means of the switches between the feeders 
and the various pairs of mains supplied by them. 

Mains and Taps.— From the panel board the mains run to cut- 
out boxes; and there the mains branch out into the taps, going to 
the outlets and supplying the lights. These circuits are designed 
for a 1.5% loss, and in small installations may be brought down 
to 1%. This gives in large plants with long runs a total voltage 
loss of about 3.5%, and for smaller plants about 2.5%. 

The lights will be supported on a fixture or a drop cord, and 
will usually be controlled by a-key socket. 

From this it will be seen that there may be from the service to 
the lamp the following succession of conductors and safety devices : 

Service connection, service wire, double-pole cut-out, double-pole 
knife switch, trunk-line to switch board, double-pole knife switch, 
fuses to protect the feeder, feeder to distributing panel box, double- 
pole. baby knife switch, fuse to protect: the main, main to the 
cut-out box, plug or inclosed fuse to protect the branch, taps to 
the outlets through single-pole snap switch to control light or 
group of lights, wire to the fixture or rosette, fixture wire to socket, 
key switch in the socket, and finally the lamp, as indicated in 
Fig. 333. 

The number of tap-circuits will be determined by the under- 
writers’ rule that no group of lights requiring more than 660 watts 
shall depend on one cut-out. Fuses and cut-outs must not be con- 
cealed in the canopies or shells of fixtures. 

Another rule of the underwriters requires a fuse to be placed 
at every point where a change is made in the size of the wire, 
unless the cut-out in the larger wire will protect the smaller. It 
is well, therefore, to lay out the wiring so that while obeying 
this rule there will not be too many fuses in series located at 
different points, which always cause delay in case of trouble. 


386 


é ‘ON YaGas4 
ee) 
asna 


qavidvL 


SdWY1‘d 0 9b XIS NVHL SYOW LON 


HOLIMS 310d-J19NIS 


ELECTRIC VL IG (VG. 


SERVICE LINE 


asna 


SNM MNNYL 
ae 
HOLIMS 


i 


SWITCH BOARD 





"A OLE ‘d’O OL 
SdWV7 Z 
syaisnio 


L3aN00S Alay 


91d 


nc 





1no 


Fig. 335. 


/ eee 
[e; 
KEY / 


SOCKET 






| "ON ¥5dG334 


PANEL| BOX 











g Vt HONVYS 


SYyIM SYNLXI4 





AGWVT ‘A OLE “dO 9L-ZE C 
"3 ‘1 LLVM 099 AlddNS NVO HONVYE HOVA 


L4ax908 Adam 


FLEXIBLE CORD 
“4 


PENDANT 
OR DROP LIGHT 


3113809 


TAP 1AAB 


Scheme cf Interior Wiring. 
























VV HONVYUa 


The number of fuses in 
series must be kept down to 
the minimum, and they should 
be centralized as far as pos- 
sible to aid the rapid location 
and replacement of the fuse, 
in case it blows. 

Inthe calculation of wiring 
the following simple formulze 
will be all that is necessary 
for the direct current system 
and for the secondary wiring 
of alternating systems. 





TOS SON Wx ae 
m= : 
v 
v 
FS ——— 
ZA Kee 
c.m. = circular mils. 


d=the distance, i.e. the 
length of wire in feet on one 
side of the circuit between the 
points in question. 

c = load carried by the wire 
in amperes. 

¥ = Volts to abe lost im the 
line. 

T = Lesistanices pels toOtman 
the wire to be used. 

10.8 = resistance of one mil- 
foot of commercial copper at 
Doe 

When the circular mils or 
the resistance per foot of the 
wire has been determined, find 
the size of the wire to be used 
by reference to the table on 
page 8, taking the nearest size 
larger than the wire as calcu- 
lated. Then refer to the table 


INTERIOR WIRING. 387 


on page 15 to see if the current that is to be carried is below the 
allowable value. 

Safety Devices in interior wiring are of special importance, 
since the inconvenience of repairing circuits is great, and the con- 
sequences of overheating wires by excessive current are likely to 
be very serious. On sevzes circuits some form of czt-out (p. 25 
and p. 340) is applied to each lamp to short-circuzt it if by accident 
it tends to interrupt the circuit. In this case the continuzty of the 
circuit must be preserved since the voltage is usually very high, 
and a long, dangerous arc would be formed if attempt is made to 
open it at any point. Furthermore, there is little risk of the cur- 
rent (in amperes) varying much from its normal value, since a 
special regulator is provided (p. 171, p. 186 and p. 189) to main- 
tain a nearly constant current. 

On the other hand, faralle/ distribution, usually operating at 
practically constant potential, requires the main conductors as well 
as each branch to be protected by a device that will ofex the par- 
ticular circuit whenever the current in it tends to become exces- 
sive. In this case the number of amperes is inversely proportional 
to the resistance of each branch circuit. 

If this resistance is reduced abnormally by a ijeak or short cir- 
cuit between the + and — conductors, the current may rise to 
many times its safe value, and the wires may be greatly over- 
heated, even to the fusing point, since the heating effect increases 
as the square of the current. For protection against this danger, 
fuses and circuit-breakers are employed in large numbers, there 
being hundreds of the former in any parallel system of distribu- 
tion of even moderate size. These two devices are discussed in 
Vol. I. Chap. XXII., but it will be well to supplement that general 
discussion by considering the particular forms used in connection 
with interior wiring. 

In principle, safety fuses are weak links purposely introduced 
into the: circuit; and intended to mélt and open it if the current 
tends to exceed a certain safe limit. Lack of confidence in fuses 
is often expressed by those who have had much experience with 
them ; but on account of their simplicity and cheapness they are 
used almost universally except on switchboards or in connection 
with motors, or in other special cases where the importance of the 
circuit or the likelihood of its being overloaded are sufficient to 


388 ELECTRIC LIGHTING. 


warrant the use of circuit-breakers. For the numerous branch 
circuits in electric-lighting, carrying only a few amperes each, it is 
practically necessary to adopt fuses. Furthermore, it is a fact that 
the use of fuses of standard lengths and cross-sections under defi- 
nite conditions will give uniform and reliable results. Formerly 
the length of the fuse wire was not defined, and it was sometimes 
open and sometimes inclosed so that it might carry much more 
current in one case than in another. 

The principal forms are “ink, plug and inclosed fuses. A 
standard type of link fuse block made of porcelain is illustrated in 
Fig. 334, and the fuse itself in Fig. 835. These are suitable for 





Fig. 384. 


circuits having a potential not exceeding 125 volts across one fuse 
link and a maximum capacity of 75 amperes. Larger and heavier 
blocks are made for greater capacities, and are provided with mica 
sheets as covers. This form requires the use of a screw-driver in 
replacing a fuse, and this in unskilled hands, or even in skilled 
ones, may by accident cause a short circuit. 

In Fig. 836 is shown the Edison porcelain plug cut-out. These 
have a maximum current capacity of 830 amperes and a maximum po- 
tential of 125 volts across one fuse. The fuse 
is contained in a screw plug, shown in Fig. 887. 
When a fuse has blown, the plug is unscrewed 
and a new one put in its place. This is a very 





simple and safe operation, even if the short cir- 
cuit still exists when the new plug is screwed in. 





Fig. 337. Edison Plug Cnt-Oat, 


INTERIOR WIRING. 389 


The zzclosed fuse represented in Fig. 358 possesses the same 
advantage in convenience and safety of renewal. It is also claimed 
to be more definite in its action, 
since the conditions are more nearly 
uniform than in the case of open 
or partly open fuses. Still another 
advantage is the fact that a fuse 
closely surrounded.with solid, f- 
brous, or powdered material, has a 
greater capacity for heat than if it 
were isolated. Consequently it re- 
quires a little longer time to reach Fig. 338. 
the fusing point, and an excess of 
current must be very great in amount, or must flow for an appreci- 
able time, in order to “blow” the fuse. A current that only mo- 
mentarily exceeds the normal will not injure the wires or apparatus, 
and it is simply a nuisance to have it 
opensiheicireult, “Lhesform «of fuse 
illustrated in Fig. 339 is very conven- 





iently replaced, and is also capable of 
being used as a sort of switch to open 
and close the various circuits. It is pro- 
vided with a copper blade at either end, 
which fits into clips just as in an ordi- 
nary knife switch. A similar arrangement is shown in Fig. 340, 





Fig. 339. 


the fuses being carried in por- 
celain boxes with projecting 
blades that are pressed into the 
clips in the cut-out cabinet. 
Circuit- Breakers. — These 
devices are shown and described 
in Vol. I. Chapter XXII., and 
belong more to the generating 
plant and switchboard than to 














interior wiring. Essentially 
they are switches that are con- 
trolled by an electromagnetic 
device so as to open automatic- 
ally when the current exceeds a certain limit. They are much 





390 BLECTRICMUCHIING 


more accurate in this respect than a fuse, and can be adjusted to 
act at any given current within a considerable range. Their accu- 
racy and adjustability are important, but their great advantage over 
the fuse is the facility of resetting 
them compared with the trouble and 
delay of renewing a fuse. The fact 
that a circuit-breaker flies open the 
instant that the current rises above 
the value for which it is set, may be 
a doubtful advantage. This might 
happen very often when the excess 
of current does not last long enough 
to cause any harm, as explained in 
connection with fuses on the preced- 
ing page. The main circuit-breaker 
may open at the same time as one in 
a branch circuit, thus shutting off 
other parts of the system needlessly. 
In some forms the so-called time 
factor is purposely introduced, a device being added to prevent 
action unless the overload is of a certain duration. An example 
of circuit-breaker illustrated in Fig. 341, differs from most types 
in the fact that the arms for the two sides of the circuit are in- 
dependent, so that one may open automatically if it is attempted 
to close the other while a short circuit still remains. 
Switches. — The general facts concerning these important de- 
vices are set-forth in Vol. I. Chapter XXII., but there are certain 
additional points to be noted in connection with interior wiring. 
The rules for switches as laid down by the National Electrical 
Code will be found on pages 9, 10 and 23 of the Appendix to the 
present volume. Ordinarily the type used on switchboards is the 
simple lever £uzfe-switch. Vhey are sometimes made in the guwzck- 
break form in order to reduce the duration and therefore the burn- 
ing effect of the arc produced on opening the circuit. It is a fact, 





Fig. 341. Automatic Circuit-Breaker. 


however, that switches are used to c/ose the main circuits or those 
carrying heavy currents, but should not be used to open them 
except in emergency. In starting up an electrical plant, or in 
closing the service switch of an installation, the switches controlling 
the various circuits may be closed before or after the current is 


INTERIOR WIRING. 391 


turned on, and a switch may be left open if no energy is required 
in the corresponding circuit. In case of overload, a circuit-breaker 
or fuse should be provided in each main or branch circuit to open 
it when the current exceeds a safe value, but the switch itself 
when carrying heavy current is to be opened only as a 
last resort. Under ordinary circumstances the lamps 
are disconnected in comparatively small groups by 
means of snap switches, one of which is shown in Fig. 
342. In fact, the current allowed in each branch cir- 





cuit is limited by the insurance rules, being a maxi fig, 342,— 
mum of 660 watts (equivalent to 12 lamps of 16 c.p. S"aP-Switeh. 
each at 110 volts). Even in a theater or other place where many 
lamps are turned on or off at about the same time, it is customary 
to control them in groups, each having a separate switch. If the 
current does not exceed 8 amperes at 110 volts a single-pole 
switch is allowed, but for currents greater 
than this it must be double-pole. 
Lreak-down Switch. A building having 
its own generating plant may be provided 
with a connection to the street circuit of 
some electric lighting company. In case 
OleaccicentetO,. Or repain of, the isolated 
plant, current may be obtained from the 
central station. The switch which enables 
this to be done is called a “break-down ”’ 
Switch, since it is used in case the local 
machinery is broken down. It is usually 
of the double-throw type (Fig, 343); and 
since street circuits are often three-wire 





Fig. 343. Break-down Suicch. 


systems, and isolated generating plants are operated in most cases 
on the two-wire plan, the switch is generally arranged to convert 
from the former to the latter, as described on page 82. 
‘Multi-Control Switches. Ut often happens that it is desired to 
light or extinguish a given lamp or group of lamps from two or 
more different points. A common case is that of a lamp which 
may be turned on at the foot of a staircase and turned off at the 
top, or vice versa. This may be accomplished in various ways: one 
plan indicated in Fig. 344 requires a three-way key socket at the 
lamp, a three-way switch at the other point of operation, and an 


392 ELECTRIC TIGHLING. 


- 


extra wire between them in addition to the two mains that supply 
the current. With this arrangement the lamp may be lighted 
or extinguished by either switch. 








TRree -Way Switch Three-way Socket 
Fig. 344, 


Panel Boards and Cut-out Cabinets are miniature switch-boards 
or sub-centers of distribution which afford means of splitting up the 


mains into branches and of grouping the cut-outs. The various 
forms used differ mainly in the styles of switches or cut-outs and 





Fig. 345. Panel Board. 


in their arrangement, as illustrated in Figs. 340, 345 and 846. The 
two or the three main conductors are represented by parallel wires 
or bars of metal, from which the branch circuits are led out 
through switches and cut-outs. ) 

Fixtures and Sockets. — The endless variety of fixtures used for 
supporting arc and incandescent lamps may be classed as furniture 





INTERIOR WIRING. ' 393. 


or ornament, as they are not of a character to be included in a 
technical treatise ; the only technical features they contain being 
the fixture wiring and the insulated joint interposed between the 
fixture and the gas-pipe to which it may be attached. The sockets 
are described in the next chapter, on Incandescent Lamps. In a 
general treatise it is impossible to go into the details of interior 
wiring, as they depend largely upon the conditions in each particu- 





Fig. 346, Cut-Out Cabinet. 


lar case. The principles involved and the chief elements of con- 
struction have been set forth, and for further information refer- 
ence may be made to the National Electrical Code printed in full 
in the Appendix and to the following publications : — 

Cushing, H. C., Jr., Standard Wiring for Incandescent Light 
and Power, pp. 116, N. Y., 1900. 

Emmet, W. L. R., Alternating Current Wiring and Mestribu- 
LOA; DDO aN aN oh 898. 

Leaf, H. M., [utertor Wiring of Buildings, pp. 195. London, 
1899 (gives English Practice). 


394 ELECTISACILIGHIING 


Noll, A., How to Wire Buildings, pp. 162, N. Y., 1899. 

Pierce and Richardson, Vational Electric Code (Explanation of), 
DpM22cjgN anes 

Robb, R., Electric Wiring, pp. 183, N. Y., 1896. 

A series of articles on /utertor Wiring, by Charles E. Knox, in 
the American Electrician, N. Y., 1898 to 1900. 


INCANDESCENT (LAMPS. ogo 


C@.EeAshel PR Vell, 


INCANDESCENT LAMPS. 


AN incandescent electric lamp is one in which light is pro- 
duced by the passage through a solid conductor of a current 
sufficiently strong to raise it to a temperature of incandescence. 
In this case the conductor is solid and continuous, while in an 
arc lamp, the other important type described in Chapters XIV. and 
XV., light is produced at a gap in the circuit across which the 
current is carried by the heated vapor present. The ordinary type 
of incandescent lamp, enormous numbers of which are now used, 
consists essentially of a high resistance carbon filament hermet- 
ically sealed in a nearly perfect vacuum. In fact, these words are 
substantially the same as the patent claims of Edison,* who de- 
veloped the incandescent lamp as well as the necessary generator 
method of distributing current and the various auxiliary devices 
to a condition of commercial success. 

Many forms of incandescent lamp have been devised employ- 
ing filaments composed of materials other than carbon, and not 
requiring a vacuum; but these are special types that will be 
described later. The present chapter is confined to the ordinary 
incandescent lamp, as already defined, which has been used to 
the practical exclusion of any other form since the introduction of 
incandescent lighting in 1880. 

Materials Used for Filaments. —In the earlier lamps made 
by Edison, the filaments consisted of platinum wire, but that metal 
soon lost its strength, even at normal working temperature ; and if 
accidentally raised above this point it was likely to be melted. 
The high cost of platinum is also a serious objection to its use 
for this purpose. Consequently Edison soon substituted carbon 
for platinum in his lamps. After trying many materials, carbonized 


* US. Patents, 1570. 


396 ELECTRIC LIGHTING. 


bamboo was adopted, and generally used in the Edison lamps 
made for about fifteen years. Other manufacturers employed | 
thread, thin strips of cardboard, or some special compound in 
place of bamboo. In practically all cases some organic substance 
carbonized by heat has been used. 

For several years the tendency has been to adopt almost 
universally the so-called “squirted filaments.” They are usually 
made by dissolving cotton in a solution of zinc chloride producing 
a viscous, semi-transparent liquid in which the appearance and 
fibrous character of the cotton are entirely lost. This gelatinous 
material is forced or squirted through a small hole, and received 
in a vessel containing alcohol, which causes it to set and harden 
sufficiently to be handled afterwards. After washing, the material, 
having the appearance and consistency of cooked vermicelli, is 
wound upon a large drum and dried, after which it possesses 
considerable strength, and looks much lke a cat-gut string such 
as is used on a violin. It is then cut into lengths suitable for 
filaments, and carbonized at a high temperature. 

The advantage of using this product in place of some solid 
substance, such as bamboo, is the fact that it is perfectly homo- 
geneous, and can be made readily and accurately of any desired 
cross-section or length. On the other hand, there is considerable 
difficulty in eliminating entirely bubbles of air from the viscous 
solution of cotton. If they are present, even though very small, 
they will cause a flaw in the filament at any point where a bubble 
may happen to exist. In order to get rid of them the solution is 
filtered and heated: under a vacuum. ‘To avoid the presence of 
impurities and to insure a perfectly homogeneous product the best 
quality of cotton wool should be used, the specially high grade 
employed by surgeons as absorbent cotton being adopted by the 
best manufacturers. Great skill and care are required in making 
the mixture, the exact density and temperature of the zinc chloride 
solution as well as the proportion of cotton dissolved in it being 
matters of particular importance. The formation of lumps in the 
jelly-like mass is likely to occur, and should be prevented by con- 
stant stirring, otherwise the resulting filaments will not be of 
uniform cross-section. 

Measuring and Sorting the Filaments. — After being carbon- 
ized, the filaments are carefully measured and sorted according to 


INCANDESCENT LAMPS. 397 


length and diameter. The latter is reduced very greatly by the 
processes of drying and carbonizing, so that it must be determined 
very exactly by means of a micrometer. A filament made from 
“< squirted ” cellulose solution is somewhat elliptical in cross-section 
owing to its having been wound, while soft, upon the drying-drum. 
For this reason it is necessary to measure both maximum and 
minimum diameters in order to determine its true cross-section. 
The filaments suitable for the various types and sizes of lamps are 
thus selected. Ina general way the length is proportional to the 
voltage, and the surface is proportional to the candle-power for 
which the lamp is intended. 

Flashing or Treating the Filaments. — The object of this pro- 
cess is to render the filaments stronger and more uniform. — For- 
merly, when they were made from bamboo, thread, and similar 
materials, the filaments obtained were far from uniform throughout 
their length. The present forms of “squirted” filaments are 
better in this respect, being more uniform in diameter and more 
homogeneous ; but even these require to be treated after being 
carbonized. The treatment consists in raising the filament to 
incandescence by passing through it an electric current in an 
atmosphere of hydrocarbon vapor or gas. 

The high temperature of the filament decomposes the hydro- 
carbon, and causes carbon to be deposited upon it. This deposit 
occurs over the entire surface of the filament, but is greater at 
any point where the electrical resistance may be abnormally high, 
because the temperature there will also be higher. Hence the 
tendency is to produce a filament of uniform resistance throughout 
its length. In the same way the strength is made more uniform, 
because any part thinner or weaker than the rest is likely to have 
a higher electrical resistance, so that it will be reinforced by receiv- 
ing a heavier deposit of carbon. On the other hand the deposited 
carbon is graphitic in character, and has a lower specific resistance 
of 10 to 15 per cent that of the original filament, which is undesir- 
able especially for high voltage lamps. | 

The filaments are treated after they have been carbonized, but 
before they have been mounted, the process being performed in a 
jar containing hydrocarbon vapor. The stopper of the jar carries 
metallic holders into which the. ends of a filament are inserted, 
the latter being then introduced into the jar. By means of the 


398 ELECTRIC LIGHTING. 


metallic holders which serve also as electrical connections, a cur- 
rent is caused to flow through the filament in order to bring it to 
incandescence. The resulting deposit of carbon reduces the resist- 
ance until a certain value is reached, when the current is inter- 
rupted, and the filament is taken out, to be followed by another and 
soon. The proper resistance is predetermined by experience or 
calculation for each type of lamp. It may be measured during the 
process of treatment by disconnecting the filament from the cur- 
rent supply, and connecting it to some resistance measuring device, 
such as an ohmmeter, a double-throw switch being used to make 
the change. In this case the measurement is made while the fila- 
ment is cold, and it is generally assumed that at working tempera- 
ture the resistance is reduced one-half. It is also an easy matter to 
determine the resistance when the filament is incandescent, and the 
carbon is being deposited upon it. By measuring the voltage across 
the terminals of the filament and the current flowing in it, we know 
from Ohm’s law that ohms = volts + amperes. In another method 
the filament is made one arm of a Wheatstone bridge, and the 
other three resistances are so adjusted that no current flows in the 
galvanometer circuit when the filament reaches the proper resist- 
ance. A relay put in place of the galvanometer will release its 
armature at that moment, and may be arranged to stop automati- 
cally the current through the filament. The increase in diameter 
resulting from the deposit of carbon is about 10 per cent, but 
varies in different sizes and makes of filament. 

Mounting the Filaments. — In order to mount the filaments, 
that is, connect them to the “leading-in” wires (CC in Fig. 352), 
that are to supply them with current, various methods have been 
devised and used. One plan consists in electroplating a sleeve of 
copper around the end of the filament and of the wire, thereby 
mechanically binding and electrically connecting them together. 
In lamps formerly made from carbonized cardboard, the ends of 
the filaments were enlarged so that they could be attached to the 
ends of the wire by very small bolts. Another method consists 
in forming a socket at the end of the wire into which the end of 
the filament is inserted, and held in place by squeezing the 
socket around it. These means of connection have been in 
most cases abandoned for the simpler and cheaper joint, made 
by pasting together the ends of the filament and wire, using a 


INCANDESCENT LAMBS. 399 


mixture of powdered carbon and molasses, or other similar sticky 
material. Still another form of joint is made by heating the 
junction of the filament and the wires by an electric current 
in an atmosphere of hydrocarbon gas or under a hydrocarbon 
liquid. In this way a deposit of solid carbon is formed around 
the filament and wire, which binds them together. The deposit 
takes place more rapidly in the liquid, but the latter is objection- 
able because it adheres to the filament and wires. ‘This so-called 
deposited carbon joint is a very good one, but is more troublesome 
and expensive to make than the pasted joint. 

Platinum “ Leading-[n ”' Wires. —‘To insure a perfectly air- 
tight seal where the “leading-in” wires pass through the glass, 
they are made of platinum, because its coefficient of expansion by 
heat agrees with that of the glass which is used. If the two 
coefficients of expansion differed materially, it is obvious that there 
would be a tendency either to crack the glass or to let in air when 
temperature changes occurred. 

Platinum being a very expensive metal, even the small amount 
required in an incandescent lamp is a considerable item in the 
cost, so that many attempts have been made to substitute some 
cheaper metal or alloy. While alloys having about the same 
coefficient of expansion as that of glass can be made, they are 
open to the objection of not being able to stand the high tempera- 
sure of melting glass or the action of the blowpipe flame without 
melting or burning while being sealed in, so that there is likely to 
be a leak owing to the imperfect fusing of the glass to the wire. 

In order to economize as much as possible in the cost of plati- 
puinetorecacilainp,. ine oteatcr portion) of sthe wlength, ofthe 
leading-in wires is composed of copper, platinum being used only 
where the wire passes through the glass. [or example, in Fig. 
302, the longer parts, D C, of the leading-in wires are of copper, 
and the shorter parts, D £, are of platinum, the joints between the 
two being made by electrical welding. 

Glass Portions of Incandescent Lamps. — The several steps in 
their manufacture are indicated in Figs. 847-353, a standard 
Edison 16. c¢. g. lamp being represented on a half scale. To 
Yee Nemannside. parigas an Plass tubers 1s) used,” beings first 
softened by heat and flared out at one end 4. ‘The other end is 
then softened, the leading-in wires C & introduced, and the plastic 


400 








Manufacture of Incandescent Lamps. 


ELECTRICALICH ING: 








Figs. 347-358, 


INCANDESCENT LAMPS. 401 


glass is pinched around the wires at YD so as to form a her- 
metical seal. If the filament is to be of a form to require it, an 
anchor / is introduced at the same time. The next step is the 
making of the bulb G, which is simply blown on the end of a glass 
tube H7/, in the ordinary way. The extreme end of the bulb is 
then heated by a blow-pipe, and a small glass tube ZL J is 
attached to it at that point. The bulb is now disconnected from 
the tube / by melting the latter around at A and pulling the two 
apart. 

The inside part 4 upon which the treated filament /V has been 
mounted by means of pasted joints at & £& F, is next introduced 
into the bulb G, and the two are united by fusing together the 
circular edges L B and K Kk. The partially completed lamp is 
now ready to be exhausted of air through’the tube Z JZ, 

The Objects of the Vacuum produced in the bulb of an incan- 
descent lamp are: 

1. To avoid the combustion of the carbon filament. 

2. To reduce wear on the filament due to “air-washing.” 

3. To diminish the loss of heat from the filament. | 

4. To decrease the flow of current in the space around the 
filament. 

At various times, it has been attempted to attain the first 
of these objects by using an atmosphere of some gas or vapor, 
such as nitrogen or bromine, which it is expected will not com- 
bine with the carbon. But even a small quantity of any gas 
left in the bulb may tend to consume the carbon, partly by 
~ chemical combination, and partly by a mechanical action called 
air-washing that wears away the filament. The presence of any 
gas or vapor also causes a more rapid transfer of heat, by conduc- 
tion and by convection from the filament to the bulb. In a 
vacuum, on the other hand, the filament loses heat by radia- 
tion alone, so that a smaller quantity of energy is required to 
maintain it at a certain temperature and candle-power. Hence 
the efficiency is improved, being inversely proportional to the 
energy consumed, other things being equal. or the same reason 
the bulb of a vacuum lamp is cool enough to touch with the hand, 
even while burning, and will not ignite anything that may come 
in contact with it unless the heat is allowed to accumulate by 
leaving it for some time partly or completely surrounded by an 


402 ELECTRIGQIICHTING. 


inflammable material, such as cloth or wood. The bulb of a lamp 
containing some gas becomes considerably hotter, and is therefore 
less convenient to handle, as well as more likely to start a fire. 
The ‘air-washing ” effect is not considered to be as important as 
formerly, the wearing out of the filament being due chiefly to pro- 


) 


jection of particles from its surface, and chemical action upon it 
if any active gas is present. 

The flow of current through the space around the filament 
is called the ELdzson effect, having been first observed by him. 
It is a loss of energy, since the pale bluish light that it produces 
adds little or nothing to the candle-power. This flow is greatly 
reduced when a nearly perfect vacuum is reached. In fact, lamps. 
are tested to see if the vacuum is sufficiently high, by connecting 
them to an induction coil; those showing the pale glow through- 
out the bulb being rejected. On the other hand, the presence of 
any considerable quantity of gas would also stop the wasteful cur- 
rent, so that for this reason alone either a very high or a compara- 
tively low vacuum is desirable. ‘The flow of current by the Edison 
effect may take place without the blue glow, but Mr. J. W. How- 
ell has shown * that the two often go together. | 

The blackening of the bulb which gradually occurs while the 
lamp is burning was found by Prof. W. A. Anthony + to be con- 
siderably less in lamps containing a slight atmosphere of bromine 
than in ordinary high vacuum lamps. The transfer of carbon from 
the filament to the bulb seems to occur as a sort of projection of 
particles along straight lines in a manner similar to the Crooke’s 
effect. Hence it is quite natural that the presence of even a small 
quantity of vapor would interfere with the deposit by reducing the 
“mean free rath” of the particles. The blackening of the bulb 
by the deposit of carbon upon its inner surface is one of the impor- 
tant causes in the falling off in candle-power of lamps. This 
matter will be considered further under the head of “ Relation 


b] 


between Candle-Power and Age” on page 416. 
The methods of exhausting bulbs used singly or in combination 
are as follows: 


1. By means of mercury pumps. 


* Trans. Amer. Inst. Elec. Eng., vol. xiv. p. 27, Feb., 1897. 
+ bid. vol. xi. p. 132, March, 1894. 


INCANDESCENT LAMEBPS. 403 


2. By means of mechanical pumps. 

3. By the so-called chemical process. 

The first of these consists in connecting the tube LJ7/ (Fig. 
352) to a Sprengel or other suitable form of mercury pump capa- 
ble of producing the very high vacuum required. At first the 
quantity of bubbles in the tube of the mercury pump show that 
the air is being rapidly removed, but later the bubbles become 
fewer and smaller, until finally none are visible. This indicates 
that no more air can be drawn out under the existing circum- 
stances, but there is still considerable gas clinging to the glass, 
filament and leading-in wires. The lamp is now heated by passing 
current through the filament or by external heat in order to 
drive off these gases and allow them to be removed by the pump. 
When the vacuum is sufficiently high, the tube /J7/ is softened 
close to the bulb by a blow-pipe flame and drawn out to form the 
tip Z (Fig. 353), thus hermetically sealing the lamp. 

The second plan, employing a mechanical pump, is now cap- 
able of producing sufficiently perfect exhaustion for high vacuum 
lamps, being also used to save time and expense in removing the 
greater part of the air at first, when the final vacuum is obtained 
by a mercury pump or by the chemical process. 

In the chemical process the lamp is nearly exhausted by a 
mechanical or mercury pump, and some substance previously 
introduced into the bulb is then caused to combine with the small 
‘emaining quantity of gas. In most cases a small quantity of 
phosphorus is put in the tube ZJZ/, and ignited by heat applied 
to the outside. It combines with the residue of gas present to 
form solids or non-conducting gases which are practically equiva- 
lent to a perfect vacuum. It is found that red phosphorus, which 
is comparatively harmless, can be used instead of the yellow form, 
that would be injurious to the employees who handled it. 

Bases and Sockets. — The sealed lamp is now ready to receive 
the base which supports it, and at the same time makes the ne- 
cessary electrical connections that supply it with current. Many 
forms of base have been used, the most prominent being the Aazsoz 
standard type shown in Fig. 354. This consists of a brass shell 
formed into a screw-thread, to which one leading-in wire is soldered 
at P, and a brass button to which the other leading-in wire is 
soldered at R. To hold the parts together and insulate them from 


404 ELECTRIC LIGHTING. 


each other, the spaces between are filled in with soft plaster of paris 
as indicated by dots in Fig. 808. ‘This is allowed to harden and is 
then dried, otherwise the moisture would short-circuit the terminals. 
At present porcelain pieces are generally used instead of plaster. 

- The corresponding Edison socket, which is the same as that 
used with plug cut-outs (Fig. 8386), is made with a screw-thread 
and contact point to receive the base of the lamp and make elec- 
trical connections to it. Simplicity and cheapness are the chief 


Edison. Sawyer-Man or United States or Thomson-Houston. 
Westinghouse. Weston. 









































































































































































































































































































































































































AMM 





ult . HI il i { Fill Mt 
or English Brush-Swan. Mathei-Perkins. Schaefer. 


Ediswan 


Figs. 354-861, Typical Lamp Bases. Two-thirds Size. 


advantages of this form; and it is gradually displacing other 
types in this country. 

The Sawyer-Man or Westinghouse lamp base, illustrated in 
Fig. 355, is provided with electrical contacts similar to those of 
the Edison type; but the lamp is held in place by inserting it in a 
socket consisting of spring clips or fingers which grasp it on all 
sides. The Thomson-Houston base has a central hole in which a 
thread is cut, so that it may be screwed down upon a projecting 
screw in the socket. The Swan, and similar bases represented 
in Figs. 8358-360, are of the bayonet type, having small pins on 
the sides which fit into slots in the socket, being inserted and 
then turned slightly in order to lock them. All of these may be 
classified under the three heads of the screw, clip, and bayonet 


INCANDESCENT LAMPS. 405 


types. The first class possesses the advantages that have been 
given for the Edison base, and the lamp may be lighted or ex- 
tinguished by screwing it in or out about one turn. This is con- 
venient in case the switch is not easily reached or is out of order. 
The clip or bayonet bases are not adapted to be used in this 
way; on the other hand, they are not so likely to work loose as 
the screw forms. For very large lamps, special types of socket, 
as in Fig. 368, are often employed. 

It has been attempted to secure the general adoption of a 
standard lamp base and socket ; but owing to patent questions, the 
jealousy of manufacturers, and the fact that large numbers of the 
different types have been installed, the effort has not been very 
successful in this country or abroad. Now that the original 
patents have expired, it would seem that this uniformity might be 
attained in order to save makers and dealers the trouble and ex- 
pense of carrying in stock so many styles of lamps and sockets. 
The great variety in voltage, candle-power, form and color of 
bulb, and type of base, makes almost innumerable combinations 
that may be called for. 

Forms of Filament. — The ordinary 16 candle-power lamp at 
110 volts consumes about } ampere, consequently its resistance 
must be about 220 ohms when burning. A filament having this 


Single Single Curl Double Double Double Curl 
Curl Anchored U Curl Anchored 





Single U 


Figs. 862-367. Different Forms of Filament. 


resistance, and sufficient cross-section to give mechanical strength 
and the required illumination, should be about 7 to 9 inches long. 
The single U shape (Fig. 362) was generally adopted in incan- 
descent lamps for many years, but the excessive length of the U, 
and its tendency to droop, demand a large bulb. Furthermore, 
its distribution of light is poor, as explained later. To avoid these 
objections, the curled forms of filament are now being used almost 


406 ELECTRICOLIGHIING. 


universally. The single curl, the single curl anchored, and the 
double curl (Figs. 368, 364, and 366), are common forms in lamps 
for 100 to 125 volts, and from 8 to 50 candle-power. 
































































































































































































































































































































































































































































































































Fig. 363. Three Hundred-Candle-Power Lamp. One-third Size. 


The Filament of a 220-Volt Lamp should be about twice as 
long as and about one-half the cross-section of a standard 110-volt 
filament giving the same candle-power, because the former takes 


INCANDESCENT LAMES. 407 


one-half as much current at twice the voltage, in order to consume 
the same number of watts. Asa matter of fact, a 220-volt lamp 
requires a larger number of watts per candle-power ; consequently 
its current is about six-tenths instead of 

one-half as great. The 220-volt filament, 

with its increased length, is usually made 

in the double UY or double curl forms 

(Figs. 865-7), in order not to require a 

large bulb. 

Large Lamps of 100 to 3800 candle- 
power are usually made with the single 
VY filament, as represented in Fig. 368, or 
with the double UV form (Fig. 865). In 
this case the cross-section is much greater, 
the current in a 100 candle-power lamp | 
being about six times that in a 16 candle- 
power lamp of the same voltage. 

Anchored Filaments are used when 
their length or the form of the bulb is 
such that there is danger of their touch- 
ing the glass and cracking it so as to let 
in the air and burn up the filament. This 
occurs either from excessive vibration or 
from the gradual drooping or bending of 
the filament, which is likely to take place, 
especially when the lamp is not vertical 
and pointing downward. Two arrange- 
ments have already been described (Figs. 
303 and 867), in which the anchors are 
el tachedetOsstiess Sinner part’ through 
which the leading-in wires pass. Another 
common form of anchor is sealed in the tip 
of the bulb, being a necessity in the tubu- 
lar lamp shown in Fig. 369 to support the - 
extreme end of the filament, and prevent it from touching the 





Fig. 8369. Tubular Lamp. 


glass. 

The Distribution of Light differs greatly in the various types of 
lamp, depending almost wholly upon the shape of the filament. 
The straight single V form (Fig. 362), giving 16 mean horizontal 


408 ELECTRIC LIGHTING. 


candle-power, emits only 5.7 candle-power in the direction of the 
tip. A “long curl anchored” filament (Fig. 3864), having the 
same mean horizontal candle-power, gives 7.05 candle-power from 
the tip; and a double curl filament (Fig. 366), of the same mean 
horizontal candle-power, gives 10.1 candle-power from the tip, 
showing great variations in illuminating power in different direc- 
tions. The horizontal and vertical distribution of light is shown 
by curves in Figs. 370 and 871 for long curl anchored and double 


4, 
anit 


Mf, 
Ya ei 
HIT | 


[/ 
Hh 


Vi 
igers 
oe 


l 






Il 





Curve of Vertical Distribution 
of Candle Power 


NG CUR 
-ANCKORED FILAMENT 





NY 
i, 






\S 
\ 









(\ 


Nill 





i) 
waist 






itm: 


GLE 
MiE 
eae 
| 


i 






fi 


| 


MT 
t 


ll 


a-b posi 


m ion of 
lament shanks 
75 go° 


Cure of Horizontal Distribution Curve of Vertical Distribution. 
of 
Candle Power DOUBLE COIL Candle Power 


Figs. 870, 871. Distribution of Light. 


curl filaments respectively. The results for the five principal 
forms as ordinarily proportioned are given in the table on page 409. 

A comparison of these figures shows that the candle-power 
measured in line with the tip 1s much less in the single or double 
U-shaped filament than in the single or double curl form, the mean 


INCANDESCENT. LAMPS. 409 


horizontal candle-power being the same in all cases. The obvious 
reason for the difference is the fact that the two former expose less 
surface in that direction than the two latter. By slightly twisting 
a U filament so that it does not lie in one plane, the candle-power 
from the tip may be increased, and by shaping it with one or two 
curls the distribution of light will evidently be still more uniform. 
It is also a fact that the tip itself intercepts, or rather reflects and 
refracts, some of the light tending to pass through it, so that the 


CANDLE-POWER OF LAMPS WITH DIFFERENT FORMS OF FILAMENTS. 


CANDLE-POWER. 





CANDLE-POWER TAKEN. 


Single 
U-shaped 


Filament. 


Fig. 362. 


Single 
Curl 


Filament. 
Scheme Recs 


Long 
Curl 


Anchored 
Filament. 
Fig. 364. 


Double 
U-shaped 


Filament. 


Fig. 365, 


Double 
Curl 
Filament. 
Fig. 366. 





16 

' 16.72 
15.6 
13.8 
14.0 
14.5 
10.9 
LOL 


(a) Mean horizontal at 180 revolutions 
(4) Mean horizontal (standard method) 
(c) Mean horizontal (from curves). . 
(7) Mean spherical (standard method) 
(¢) Mean with axis at 45 degrees 

(7) Mean hemispherical : 

(¢) Mean within 380 degrees from tip . 
(2) From the tip . Sat 


16 

















candle-power in that particular direction is still further diminished. 
For this reason “tipless lamps’’ are made, the end of the bulb 
being made perfectly smooth. 

On the other hand, the table shows that the mean spherical 
and mean hemi-spherical candle-power are very nearly the same for 
all five forms of filament. Asa matter of fact, either of these is 
far more important practically and scientifically than the candle- 
power in any one direction, except for some special purpose, in 
which case a reflector may be used to throw in the direction re- 
quired nearly all of the light emitted by the lamp. The facts given 
in Figs. 870-371 and in the table are obtained from a paper by 
Professor A. J. Rowland before the Franklin Institute,* in which 
the great importance of the light from the tip is insisted upon. 
In fact, he calls this the “useful light,” because 
lamps are usually placed with the tip downward. 


incandescent 
But in many 


* Electrical World and Engineer, Oct. 18, 1900. 


410 ELECTRIGUIHGHTING 


cases they are arranged the other way; and even when they are 
not, there are reflections from the ceilings and walls, and from the 
globes or shades with which lamps are generally provided, so that 
a fairly uniform distribution of light results. 

Resistance of Filaments. — The only electrical property that an 
incandescent lamp possesses is its resistance. The ordinary carbon 
filament has about twice as much resistance when cold as it has 
when raised to the working temperature. Obviously the latter is 
the important value, and absolutely determines the current and the 
power that the lamp will consume at a given voltage. Calling the 
latter V, the resistance in ohms of the hot filament ,, the current 


in amperes (Gand the power in watts, WV, we have> +O — ae and 
Ve h 


Ordinarily lamps of almost any size take from 3 to 4 watts per 
candle-power. Assuming an average value of 3.5, and that the 
voltage Vis 110, we have from the second equation: 3.5 X c. p. 
= 12100 + R, or R, = 3457 +c. p. Hence the resistance of a 
46 candle-power lamp using 3.5 watts per candle-power is 3457 
-+- 16 = 216 ohms, the» current ‘is 110-216 ==.51 ampere,sand 
the power is 12100 + 216 = 56 watts. ‘A lamp of 32 candle-power 
consuming the same number of watts per candle-power has a resist- 
ance of 3457 + 32 = 108 ohms, or exactly one-half as much as 
before, the current is 110 + 108 = 1.02 ampere, and the power is 
12100 + 108 = 112 watts, the two latter being twice as great as 
for the 16 candle-power lamp. In short, for a given efficiency and 
voltage, the resistances of lamps are inversely proportional to their 
candle-power, and the current and power increase directly with the 
candle-power. | 

Specific Resistance of Filaments. —The completed filament con- 
sists partly of the original cellulose or other material carbonized, 
and partly of the carbon deposited upon it when it is “flashed ” or 
“treated.” The specific resistance of the former differs greatly 
according to the material used, but is ordinarily between .0022 and 
.0035 ohms per cubic centimeter when hot, and about 1} to 2 times 
greater when cold. The deposited carbon has a specific resistance 
about .12 to .16 as large as that of the untreated filament when 
both are hot, but the resistance of the former is increased about 
2 to 23 times at ordinary temperature. In almost all lamps the 


INCANDESCENT LAMBS. 411 


proportion of the two kinds of carbon is such that the resistance of 
the treated filament is about twice as great when cold as when hot. 

The variation in resistance is not great at or near the working , 
temperature; in fact, most of the reduction in resistance occurs 
before the filament becomes red hot. This is fortunate, because 
a lamp is exceedingly sensitive to variations in voltage, and a de- 
creased resistance with increased temperature would aggravate this 
difficulty. It would be desirable, in fact, to have the resistance of 
the filament increase with temperature, as in the case of metals, 
tending to keep the current constant if the voltage happens to rise 
or fall. Mr. J. W. Howell * has shown that this effect is obtained 
when the proportion of deposited carbon is large. This form of 
carbon is graphitic in character ; and its resistance falls rapidly until 
the voltage is 30 or 40 per cent of its rated value, above which the 
resistance increases steadily even at 60 per cent excess over the 
normal voltage, which is the limit of the experiments, as the lamps 
burn out very quickly at this high temperature. The resistance 
of the untreated filament does not fall so rapidly at first as that of 
the deposited carbon, but it continues to diminish even when the 
voltage is raised to 60 per cent above the normal. Hence it is 
possible, by varying the proportion of original and deposited carbon, 
to have a positive, zero, or negative temperature coefficient at 
working voltage. In most cases it is practically zero. The 
original filament of Edison lamps has a specific resistance of 1.726 
ohms per cubic mil cold, and .88 ohms at a temperature corre- 
sponding to 3.1 watts per c. p. The figures for the deposited 
carbon are .26 and .12 ohms respectively. 

Size of Filaments. — The dimensions of a filament must fulfill 
two conditions: first, the resistance must be such that the lamp 
shall take the proper current and power at the voltage for which 
it is intended, as explained on p. 410; and second, the power lost 
by the filament as heat at the working temperature must exactly 
balance the electrical power supplied. The loss of heat from a 
body may take place in three ways: (1) by conduction through 
the bodies with which it is in contact; (2) by convection currents 
in the gas or liquid surrounding it; (8) by radiation. The fila- 
ment of an incandescent lamp loses a small amount of heat by 


* Trans. Amer. Inst. Elec. Eng., vol. xiv,, p. 80, 1897. 


412 ELECTRIC LIGHTING. 


- 


conduction through the leading-in wires; and since it is usually 
situated in a nearly perfect vacuum, it loses practically nothing by 
convection, hence the loss occurs almost entirely by radiation. 
The rate at which a body radiates heat is proportional to its surface, 
other things being equal, so that this surface must have a certain 
value for a given number of watts supplied. According to New- 
ton’s law of cooling, the loss of heat is also proportional to the 
elevation in temperature, and finally it depends upon the character 
or emissivity of the surface, that is, the number of heat units 
emitted from a unit surface per degree of temperature above that 
of the surrounding bodies. Above a red heat the illumination from 
the filament increases much more rapidly than the emission of heat, 
consequently the efficiency or candle-power per watt is greater the 
higher the temperature. There is a practical limit, however, to 
the temperature, above which the filament is too rapidly destroyed, 
so that there must be a compromise between the life of a lamp and 
its efficiency. 

The actual working temperature of filaments is very difficult 
to meéasure.. According to Prof: Hie aW eberait 15 159 Gan 
3.1 watts and 1560° at 4 watts per candle-power. In practice this 
temperature is indirectly determined by the color of the light, the 
efficiency and the life of lamps, all of which depend upon it. 

The filament may be rectangular in cross-section when cut 
out of cardboard or sheets of other material, and it has sometimes 
been made hollow; but ordinarily it is solid and circular, or slightly 
elliptical in section. Ina filament having a diameter J and length 
Z in centimeters, surface S in square cm., resistance when hot £&,, 
and carrying a current C, the heat produced must be proportional 
to the surface, since it is lost almost entirely by radiation. If 
is this loss measured in watts per square cm., and ¢ the specific 


resistance per cubic cm. 


: 4 - 


Hence by substitution 


Geary, Ae SORE we ,3/ 4r 
ieee een S77) ) ee OE) Fyr2? PLY Cage) Dene \ Tie 
The quantity under the radical sign is constant for a given 


material at the working temperature, consequently J, the diame- 


INCANDESCENT LAMPS. 413 


ter of the filament, must be made proportional to the 3 power of 
the current. The length Z disappears, hence for a given tempera- 
ture (about the same for lamps using the same watts per candle- 
power) the diameter depends solely upon the current to be 
carried. The resistance A; increases directly with the length Z, 
hence C #,, or the voltage required between the terminals of a 
filament, is directly proportional to its length, other things being 
equal. For example, a 220-volt lamp may be made by doubling 
the length of a 110-voltefilament, a common plan being to use two 
of the latter in series. The current would be the same in both 
cases, hence the watts are twice as great for the 220-volt lamp, 
and the candle-power, being nearly proportional to the watts, would 
also be doubled. Two 16 candle-power filaments would give 32 
candle-power; so in order to make a 16 candle-power, 220-volt 
lamp, it is necessary to reduce the diameter of the filament, making 
it the same as for 8 candle-power at 110 volts. Unfortunately the 
weakness, due to diminished diameter, requires the lamp to be run 
at a somewhat lower temperature, and therefore lower efficiency. 
For example, a 220-volt lamp may take 3.8 compared with 3.1 watts 
per candle-power for 110-volt lamps, or about 20% more power. 

The actual sizes of filaments depend largely upon the propor- 
tion of deposited carbon, the specific resistance of the latter being 
about .12 to .16 that of the untreated filament, as already stated. 
Ordinarily the diameter is increased about 10 or 20% by the de- 
position of carbon. \ 

Relations Between Voltage, Candle-Power, Efficiency, and Life. | 
— The voltage of a lamp is the potential difference measured across | 
its terminals. Candle-power may be defined in the various ways/ 
stated on page 308, the mean spherical candle-power being the 
complete measure, but the most difficult to determine. The mean 
horizontal candle-power may be easily measured, while the lamp is 
rotated 180 to 220 times per minute with its axis vertical, and it 
is that by which lamps are rated by their manufacturers; but the 
mean spherical is usually 15 to 20% less, as shown in the table on 
page 409. It has been recommended by the National Electric 
Light Association to measure the candle-power while the lamp 
is rotated with its axis inclined 45° to the photometer. This 
usually gives results approximating the mean spherical candle- 
power, but does not necessarily do so. In what follows, the mean 


414 BLECTRIGALIGHIING: 


horizontal candle-power is used, since lamps are generally rated by 
it. The effictency of a lamp is measured by the number of candle- 
power per watt. It is usually stated as the number of “ watts per 
candle-power ;” but of course this is the inverse of efficiency, 
since it is larger with poorer lamps. ‘The /zfe of a lamp means 
either the total number of hours it gives light before burning out, 
or the number of hours it burns, until its candle-power has fallen 
to a certain fraction — usually 80% of its rated value. The former 
might be called the ¢o¢a/, and the latter the wsefu/ life, beyond 
which it is not economical, and should be replaced by a new lamp, 
even if it is capable of burning much longer. Unless otherwise 
stated, all data are given for lamps up to 125 volts, and are sub- 
stantially true for 220 volts, but the latter are more sensitive. 

The candle-power, etc., of lamps vary in much greater propor- 
tion than the voltage supplied, as shown in the following table: 


” 


ate 


VARIATION IN CANDLE-POWER, EFFICIENCY, AND LIFE. 


In the following table is shown the variation in candle-power, 
efficiency, and useful life of General Electric standard 100 to 125 
volt 3.1 and 3.5 watt lamps, due to variation of voltage supplied 
to them. 


EFFICIENCY IN E 
FF 
Per Cent PER CENT Watts Ae Wie, RELATIVE 
N oF NorMAL Per CANDLE rae x LIFE 
oF NorRMAL Canoe ? 3.1-Watr PER CANDLE, Br Waris 
VOLTAGE. 3.5 WATTS. ‘ * 


On 
PAINTER OOH 


a 
DOSMARAD 


Co NAH 
Pe RO C0: COO C2 G2) COO Ce a Or ON 
WOSHNWADUDSHNRADOW 
ARTIoDIdS BOWNSARAUSS 


4.6 
4.4 
4.2 
4.1 
3.9 
3.7 
3.6 
3.4 
3.3 
3.2 
3.1 
2.9 
2.9 
2.8 
2.7 
2.6 
2.5 


me BS 





For example, a lamp of 16 candle-power, 105 volts, and 3.1 
watts, if burned at 103 % of normal voltage, or about 108 volts, 


INCANDESCENT LAMPS. Wy: 


will give 118% of 16 candle-power, or 17.9 candle-power, the 
efficiency will be 2.8 watts per candle, but the life is reduced nearly 
one-half, being .562 of the normal. 

In other words an increase of only 3% in voltage raises the 
candle-power 18 %, the explanation being that up to a red heat no 
light is given, but after that increases rapidly with the tempera- 
ture. Since the resistance of the filament is almost constant near 
the working temperature the current rises directly with the volt- 
age, so that the watts for this case are 103 x 103 = 106 % of 
their normal value ; that is, 6 % more power produces 18 % more 
candle-power, the watts per candle-power being reduced from 3.1 
to 2.8, an improvement of 10%. Unfortunately this very desir- 
able gain is offset by the decrease in life resulting from the higher 
temperature and the rapid falling off in candle-power and 
efficiency. Long experience has shown that filaments for 125 
volts or less should be designed to run at a temperature that 
gives an efficiency of 8.1 to 3.5 watts per candle-power. Above 
this, the trouble and expense of renewing the lamps more than 
counterbalance the saving in power. It is also important to note 
that the rated watts per candle-power usually represent the zzzzzal 
efficiency and filaments that burn at too high temperature, soon 
show much poorer results, so that the average efficiency may not 
be improved. In the case of lamps for about 220 volts, it has not 
been found practicable to do better than 3.4 to 4 watts per candle- 
power (initial) owing to the greater length and smaller diameter of 
the filament as explained on p. 406. 

Another table, issued by the makers of the Packard lamp, is . 
given below, showing results somewhat different from those on 
p. 414, the average life being less affected by raising or lowering 
the voltage. For example, 3.1 watt lamps having 580 hours 
_ average life at normal voltage, are stated to have a life of 280 
hours at 6 % increased voltage. In the previous table the rela- 
tive life is given at .31, that is, 381 x 580 = 179.8 hours, which is 
considerably less. The results of actual practice probably approxi- 
mate more closely those contained in the former table. The 
usefus life at normal or excessive voltage is actually less than 
here stated with the usual limit of 80 of the initial candle- 
power. For lives as long as those given in the table, the average 
candle-power would fall to 60 or 70 4% of its initial value. 


A416 ELECTRIC 17GHIING: 


EFFICIENCY AND AVERAGE LIFE OF LAMPS AT VARIOUS VOLTAGES. 













98 PER Cent 100 PER CENT 102 Per CENT 104 PER CENT 106 Per CEentT 
oF NorRMAL oF NorRMAL oF NORMAL oF NorMAL oF NorMAL 
VOLTAGE. VOLTAGE. VOLTAGE. VOLTAGE. VOLTAGE. 





Actual | Actual Actual Actual Actual Actual Actual Actual Actual | Actual 
Watts Life Watts Life Watts Life Watts Life Watts Life 
per in per in per in per in per in 
CoEPs Hours. Cee. Hours. ‘Opa 2 Hours. Gye: Hours. Geir. Hours. 
































4.85 | 3500 4.5 2400 4.21 | 1830 3.92 | 1400 Dail, 1120 
4.51 | 2000 4. 1500 on14 | LL6O 3.48 880 3.28 710 
Sri t 113200 3.5 900 oat oy 100 3.05 550 2.87 440 
3.04 760 3.1 580 2.9 460 2.7 360 2.54 280 
2.69 350 2.5 260 2.54 210 2.18 170 2.05 140 








Individual Performance of Lamps. The discrepancies just 
pointed out illustrate the great differences in rating and in re- 
sults. This is partly due to different methods of manufacture 
and testing, and partly to wide variations in individual perform- 
ance. The figures are supposed to represent averages ; but lamps, 
even when rated exactly the same, differ greatly from each other. 
The results of tests on a number of lamps are plotted upon what 
are called “target diagrams,” as illustrated in Figs. 872 and 373. 
The former shows that the watts required to produce a given 
candle-power vary about 10%, and the candle-power runs from 
16 to 21, with watts from 63 to 71, although the lamps were all 
supposed to be the same. These are bad results; but Fig. 373 is 
considered very satisfactory, since only 2 lamps out of 50 are out- 
side of the limiting target, which permits 1.5 candle-power, and 
3 watts range above or below the normal. The manufacturer 
attempts to hit the center, that is, obtain uniform results ; and in 
this case has done fairly well with most of the lamps.  Neverthe- 
less, the individual differences are considerable, and show the diff- 
culty of rating incandescent lamps exactly. . 

The Relation Between Candle-Power and Age in Fig. 374 
also illustrates these differences, lamps of approximately equal 
initial candle-power giving from 11} to 174 candle-power at the 
end of 100 hours run. In some cases the candle-power rises at 
first, in others later, and in some not at all; but the general 
tendency is downward for all. The average shown by the dotted 
line is fairly good ; being 14.1 candle-power, or 88 % of 16 candle- 
power at 600 hours, and apparently would fall to 80% at about 


417 


66 G7 _ 6G 


LNGCANDESCENT LAMES. 
Watts 


oo 








5S 














8 GO %O 7 
57 


GA 65 


0) FREESE EEE 


Figs. 372, 373. Relation between Initial Candle-power and Watts Consumed. 






0 2 =o Cy Ot Oe a ee 


%  S  samod-s}pueD, the “wemod-e|puey rg 


418 ELECTRIG#OLI GETING. 


850 hours, a satisfactory result for a 3,5 watt lamp. The decline 
in candle-power of an incandescent lamp, which continues until 
finally the filament burns out, is due to the following causes: 

1. The filament wears away by evaporating or projecting 
particles of carbon from its surface. 


flours 


O lOO. 200 S00 A400 500 GOO 










is Gt 
A 
CECE EERE 
[ 7 ee RSS m7 ) PECE Eee 
SESSSeSSE800058 
= Perri 
Coo HH 
1 aa 
Ss ce 
in coo 
S ies 
aS an 
ag CCC 
SI] BERUSABEB 
PS RwSES we 
¢ a a a 
_ RSS 
Oo CI PSOE 
‘aE CESS 
N CeoCCeso 
1 ELE | 
\ “ root 1] 
re) PS PSEC 
CPPS 
Can poets 
coors 
is SECC 
0) b~@n EER 
CS 
— SSE 
; CPAs 
O Serer 
era 
a 
Bs 
m() Denna 
2aneES 
O CCC SCOCCH 
COCAINE PSS 
ACOA Coes 
CNET CCC BEEP> oa 
cor = Cert t 4 
Pere ce Saseeneee seecene 
SOL apy OFZ Sanaa ae 
aide seuaesn de H we - 


(re 3874. Relation vo PRR and Age. 


2. The interior surface of the bulb becomes blackened and 
less transparent, owing to the carbon deposited upon it. 

3. The emissivity (for heat) of the filament increases so that 
its temperature is lowered. 

This falling candle-power is the most serious trouble with 
incandescent lamps, since it is not shown by a test in the begin- 
ning, and being so gradual escapes definite attention. It is, how- 
ever, a common cause for dissatisfaction, producing the very 


INCANDESCENT LAMPS. 419 


general impression that a so-called 16 candle-power incandescent 
lamp does not give as much light as the ordinary gas-burner (using 
5 cu. feet per hour). This idea is well founded, because we have 
seen that lamps are rated by their mean horizontal candle-power, 
which is usually 15 to 20% less than the mean spherical. 
Furthermore, the former falls to 80 % of its initial value at the end 
of the useful life, and the average is 90 %, assuming a uniform de- 
cline, which is close enough for practical purposes; so that the 
actual candle-power is about 25 % less than the nominal, or about 
12 candle-power, compared with about 20 to 30 for the gas- 
burner. 

This trouble is aggravated by the fact that lamps are rarely 
renewed when they have fallen 20% in candle-power, as the almost 
universal custom is to let them run until they burn out, which 
may take 1500 hours or more. During the latter half of this 
period, their average candle-power is often not more than 60 or 
70 % of the initial candle-power; and the watts per candle-power 
have risen from 38.1 or 3.5 to 5 or 6, a loss of 30 or 40 % in actual 
light, and an increase in cost of 60 or 70 % per candle-power. The 
obvious conclusion is that it is uneconomical to burn lamps more 
than about 500 or 600 hours; and it would be a positive saving if 
one should break them at the end of this period ; in fact, this limit 
has been aptly called the “smashing-point ’ * It is safe to say 
that hundreds of thousands of dollars are wasted annually in the 
world by not observing this important fact. 

A further exaggeration of this bad situation arises from the 
common tendency to supply lamps with less than their normal 
voltage. A deficiency of at least 1 or 2 volts is the rule and not 
the exception, and it often amounts to 4 or 5 volts. This custom 
is the result of attempting to prolong the life of lamps as much as 
possible. It is, however, a “penny-wise and pound-foolish ” prac- 
tice, since the lamp itself costs about 20 cents, while the energy 
that it consumes costs $3.00 during a normal life of 400 hours at 
an ordinary price of .75 cent per 16 candle-power lamp-hour. A 
lamp using 38.1 watts per candle-power at normal voltage has an 
average life of 400 hours. If this lamp were burned at 98 % of 
normal voltage its life would be increased to 584 hours, but its 


* Electrica World, Dec. 24, 1892. Trans. Amer. Inst. Elec. Eng., vol. x., p. 65, 1898. 


420 ELECTRIC LIGHTING. 


consumption of energy is raised to 3.54 watts per candle-power or 
7.4% more. At .75 cent per lamp-hour and for 584 hours’ life 
the energy costs $4.38, on which an increase of 7.4% amounts to 
32 cents. The lamp burns 584 — 400 = 184 hours longer, but 
this effects a saving of only (184+ 400) x 20=9 cents, which is 
:28 as’ much “as the 7extrarcost sor fenerey,) thewnet weses bem 
32 —9= 28 cents. The sole advantage gained is the fact that 
the lamps are renewed every 548 instead -of 400 hours, but this 
saving is only a small fraction of a cent per renewal. 

This false economy is almost universal, because a man in charge 
of a lighting-plant notices each time that a lamp burns out, and 
considers it an actual loss of 20 cents. He forgets that in most 
cases the lamp has given light for 600 hours or more, and its cost 
per hour of service is only 20 + 600 = .03 cent compared with .7 
cent for energy. The importance of the latter item is only found 
by calculations based upon electrical and photometric tests, hence 
it is rarely appreciated by the ordinary user. 

In the comparisons made above, the price of electrical energy 
has been taken at the rate charged by central stations, which varies 
from .5 to 1 cent per hour for a 16 candle-power lamp consuming 
50 to 55 watts, an average rate being .75 cent. For isolated 
plants, in which the energy is generated on the spot, its cost may 
be only .15 to .25 cent per lamp-hour; but even then the extra 
energy required at 98% of normal voltage is one-fifth to one-third 
as much as before, or 82 + 5 to 82 + 3 = 64 to 10.7 cents for 554 
hours, compared with a saving in lamps of 9 cents. Further- 
more the price of lamps may be less than 20 cents. It is custom- 
ary to regard the rated voltage of a lamp as a maximum value 
never to be exceeded, consequently the inevitable variations that 
occur produce an average at least 1 or 2% below the normal pres- 
sure, and often it is 4 or 5% too low, resulting in very poor 
economy. While it is injurious to run lamps above their normal 
voltage, nevertheless the average pressure should equal that for 
which they are rated, and the regulation (i.e., uniformity of voltage) ’ 
should be good enough to avoid any serious shortening of life. 
Aside from any direct question of dollars and cents, the dissatisfac- 
tion and the depressing effect produced by running lamps beyond 

(their normal life or below their rated pressure are sufficient reasons 
; to demand very careful attention to this point. ) 


INCANDESCENT LAMPS. 421 


Approximate Formule for Relations between Voltage, Effictency, 
Life, and Candle-Power may be used within a limited range of 
about 5 % above or below the normal values, which is enough for 
any practical purpose. Calling V the voltage supplied at the 
lamp terminals, C the current in amperes, R its resistance (hot) 
in ohms assumed to be constant within the range named, W the 
power in watts consumed by it, D its candle-power, A the so-called 
efficiency “in watts per candle-power, and L the normal life or 
average number of hours to reach 80 % of the rated candle-power, 
we have: — | 


C=V+R(QA) R=V+CQ) WH=V?+R=CRE 





Corals since # is nearly constant, (4) 

Hee OC Ties Bi het ‘s - (5) 

Ao - ore 2 ore =e a a“ «<6 ‘< (6) 

DO Fas Ode Om ers ote ke a i (7) 
1 ih 1 jae 

LD rm Gm © Tar’ Edison 3.1 Watt Lamps, p. 414, (8) 


To apply the above expressions, we ‘nay find R from (2) by 
measuring V and C with volt- and ampere-meters while a lamp is 
burning. From (4) we know that a certain increase or decrease in 
voltage, say 2 %, produces the same change in the current and (5) 
shows that the watts are proportional to the square of either volt- 
age or current. From (6) we find that a lamp consuming 3.1 
- watts per candle-power, at rated voltage, requires at 98 % of that 
voltage 3.1 + .98+ = 3.1 + .922* = 3.386 watts per candle-power. 
This agrees closely with the value 3.34 given in the table on p. 414. 
From (7) its candle-power is found to be .98° = .886 of the normal 
compared with .89 in the table and from (9) its life is 1 + .9829 =1.5 
times normal compared with 1.46 in the table. These formule, 
as already stated, are merely approximate, and do not apply to 
individual lamps, but they bring out very important and interesting 
facts that are practically true when a number of results are 
averaged. 

Special Lamps. — Almost innumerable varieties of lamps are 
made for different purposes. The standard voltages are 50 to 60, 
100 to 120, and 200 to 240 for central station or isolated plant 


422, ELEGLIRICMIGH LING: 


lighting ; but many others between and below these limits are also 
adopted. Prominent among these special types are the low-voltage 
lamps for use with storage or primary batteries, and ranging from 
3 to 12 volts. In the larger sizes these are made like 
the standard lamps; but for the smaller sizes they 
are given special forms, as, for example, the bicycle 
lamp in Fig. 875, giving ? candle-power, 
and consuming .0 ampere at 4 volts. The 
surgical lamp, shown actual size in Fig. 
. 376, represents one of the very smallest 
Fig. 376. forms, requiring 38 volts and about 1 am- 
eds ia ae ae pere, and giving } candle-power. 

Another important class of low-voltage 
lamps includes the so-called series lamps. They are used in a 
candelabra or sign in order to subdivide the light and also simplify 
the wiring. They may be connected in series across an ordinary 
110 volt or other constant potential circuit. It 
is necessary that the members of each series 
should be designed for the same current within 
.03 ampere. The lamps may differ in voltage, 
but the sum of the voltages in any series must 
equal that of the circuit within 3 volts. The 
lamp represented full size in Fig. 877 gives 1 
candle-power, and consumes .33 ampere at 12.5 
to 15 volts, being run 8 in series on 100 to 120 
volts. 





Series lamps are also made for constant 
current circuits as described on pp. 24, 25, and 
in Chapter X. For a 10 ampere series arc 





Fig. 877. Series Lamp. 
circuit they require about 4 volt per candle- 


power, and for the 8 or 8.5 ampere alternating or direct current 
circuits they use about 1 volt per candle-power ; in either case the 
filaments are made sufficiently large to carry the current. 

In addition to the many different voltages for which lamps are 
made, several different sizes are supplied for each voltage, the 
standards being 8, 16, 24, 32, 50, and 100 candle-power, but others 
are often required. Various shapes of lamps are manufactured 
for special purposes, as, for example, the tubular lamp in Fig. 369, 
and some ornamental forms. Finally lamps are made in many 


INCANDESCENT LAMPS. aU 


colors, such as red, blue, green, amber, opal, frosted, etc., besides 
the ordinary clear glass bulbs. The result is that the total number 
of different styles of lamp that are made is many thousand. 

Renewal of Filaments. — In most cases whena lamp burns out or 
is reduced in candle-power and efficiency below the economical limit, 
it is the filament alone that is worn out. The bulb, base, leading-in 
wires, etc., are usually intact and capable of being used again. 
The renewal of the filament and vacuum is now carried on success- 
fully, the process being as follows: A hole is made in the bulb by 
removing the tip, and the carbonaceous deposit on the inner sur- 
face is burned off by the application of heat to the outside. The 
old filament is taken out through the aperture in the bulb and a 
new one introduced, being then connected to the leading-in wires 
by a pasted joint as described on p. 398. The joint is set, and the 
gases driven off by a blow-pipe inserted through the hole in the 
bulb. A tube similar to L M on p. 400 is attached to the bulb at 
the point where the hole was made, the parts being fused together, 
and the bulb is exhausted and hermetically sealed in the usual 
manner as described on p. 401. The brass base and the outer sur- 
face of the bulb are also cleaned if they require it, and the lamp 
then has the appearance and useful qualities of a new one. 

The so-called stopper-lamps are easily renewable, since the inner 
part (A B in Fig. 349) that carries the filament fits into the bulb 
with a tapering ground joint similar to that of a glass stopper for 
a bottle. It is cemented in place in order to hold it and also make 
the seal more nearly air-tight. This type is more expensive to 

-make than the ordinary lamp with fused joints, and does not main- 
tain the vacuum so well. 

‘¢Turning Down’’ Incandescent Lamps. — It is often urged as 
an objection against these lamps that they cannot readily be made 
to give more or less light, as in the case of gas or oil lamps. In 
the majority of instances when the latter are turned down it is to 
save the trouble of relighting them, which does not apply at all to 
the incandescent lamp. Furthermore the light of the last-named 
may be diminished temporarily or permanently in several ways. 
One plan is to substitute a lower candle-power lamp in the same 
socket, which can easily be done in a few seconds. Another 
method is to insert resistance or, for alternating currents, induct- 
ance in the circuit. The resistance or inductance is placed ina 


424 ELECTRIC-LMGHIING 


special socket and controlled by a key. A third arrangement em- 
ploys two filaments which are connected in parallel or singly for 
full light and in series for reduced effect. A form of light is made 
in which a 16 and a 1 candle-power filament are put in the same bulb, 
and either may be lighted by turning the socket slightly. An obvious 
way to dim a light is to put a shade ora less translucent globe 
around it. This fails to save any energy when less illumination is 
required, but is simple and effective. A combustible shade, such 
as cloth, paper, or wood, should never be put in contact with or close 
around a lamp, as the heat will accumulate and may start a fire. 

Specifications for Lamps.— In buying or making contracts 
for any considerable quantity of lamps it is customary to specify 
certain requirements. 

The initial candle-power at the rated voltage should not be 
more than 9% above or below the value called for. This margin 
amounts to 1} candle-power for a 16 candle-power lamp, as shown 
in Fig. 378, the “target’’ (within which the lamps, must hit) 
extending from 14} to 17} candle-power. This limit applies to the 
individual performance of every lamp, and any that exceed it may 
be rejected. The avexage initial candle-power of a certain lot of 
lamps should be within 6 % of the rated value (1 candle-power for 
a 16 candle-power lamp). It is not desirable for lamps to be 
either above or below their rated candle-power, since their life is 
shortened in the former case, and their efficiency reduced in the 
latter, and either interferes with uniformity of results. The candle- 
power is usually measured when the lamp is mounted vertically 
in the photometer and rotated at about 180 r. p. m., the result 
being the mean horizontal candle-power. ‘The relations between this 
and the mean spherical candle-power and candle-power from the tip 
are shown in Figs. 870-1. As already stated, the mean horizontal 
candle-power, being easily measured, and the one by which candle, 
oil, and gas lights are rated, is generally adopted. In some cases, 
it is specified that lamps shall not give less than 7 candle-power 
from the tip. The unit of light commonly accepted in this 
country is the British ‘Parliamentary Standard”’ candle-power. 
From this as a przmary standard a number of incandescent lamps 
are carefully rated, and serve as excellent secondary standards, 
being burned only a minute or so at a time to check other incan- 
descent lamps that are used as working standards. 


INCANDESCENT LAMPS. 425 


Life of Lamps.— Since all of the above statements refer to 
entttal candle-power, it is necessary to specify the useful life of a 
lamp, or the time it will burn before falling to a certain candle- 
power, usually 80 % of the initial candle-power. For lamps having 
an initial efficiency of 3.1 watts per candle-power, the useful life is 
about 400 to 450 hours. At 3.5 watts it is about 800, and at 4 
watts about 1600 hours. 

Candle-hours —The true measure of a lamp’s value is the 
product of its useful life in hours and its average candle-power 
during that time. The latter is usually about 90 % of the initial, 
hence a 3.1 watt 16 candle-power lamp should give at least 400 x 
16 x .90=5760 candle-hours. | 

Liffictency. — The number of watts consumed per candle-power 
is another important point in lamp specifications. It refers usually 
to initial values, the specified useful life being a check upon the 
fall in candle-power and indirectly upon the efficiency. The 
standard efficiencies are 3.1, 8.5, and 4 watts per candle-power. 
Each lamp at rated voltage should take within 6 % of the watts 
specified, and the average for a large number should be within 4 % 
of the specified figure. If the efficiency is high (i.e., small con- 
sumption of power) the life is shortened, and vice versa, a fair 
‘ compromise being adopted in practice, as explained on pp. 415 
and 418. If the cost of energy is low, as for example in some 
water-power plants, a lower. efficiency lamp may be used, but it is 
seldom economical to use 4 instead of 3.5 watt lamps. The useful 

life of the former is about 1600 hours compared with 800 for the 
latter, which would save one lamp costing about 20 cents every 
1600 hours. The energy consumed in 1600 hours costs } to 3 cent 
per lamp-hour at ordinary central station rates, or $8 to $12; and 
a 3.0-watt lamp would. use one-eighth less energy than a 4-watt 
lamp, the saving being $1 to $1.50, which is 5 to 74 times the cost 
of a lamp. Isolated electric-lighting plants in hotels, factories, 
etc., involve very little extra expense for engineers and other 
labor, or for coal when the exhaust steam is used for heating ; 
hence the electrical energy may be produced at 15 to .25 cent per 
lamp-hour. For 1600 hours it amounts to $2.40 to $4.00, and 
one-eighth of this is 30 to 50 cents, which is also greater than the 
cost of a lamp, so that even then 4-watt lamps are less economical 
than those using 3.5-watts per candle-power. It may happen that 


426 ELECTRICMIIGHUANG 


lamps are located in some inaccessible place, such as the ceiling of 
a large hall or railway station, and in that case it might be better 
to use the long-lived 4-watt lamps to save the trouble of frequent 
renewals. Where the regulation is poor (i.e., voltage varies con- 
siderably) the life is shortened, and it may be desirable to use 4- 
watt lamps. 

Bulbs and Bases. —‘Vhe former are specified to be uniform in 
size and of best quality glass, clean and free from flaws or blem- 
ishes. The metallic parts of the base should be of good quality 
brass, uniformly and accurately fitted to the bulb so as to be im- 
pervious to moisture. When placed in the socket no live metallic 
part (i.e., connected to the circuit) should be exposed. 

Vacuum. — All lamps must have a practically perfect vacuum, 
and show no glow when tested with an induction coil giving a half- 
inch spark. 

For further information regarding Incandescent Lamps, refer- 
ence may be made to the following : — 

Lhe Incandescent Lamp and Its Manufacture, by Gilbert S. 
Ram, pp. 218, London, 1898. 

A Life and Effictency Test of Incandescent Lamps, by Pro- 
fessor B. F. Thomas and Messrs. Martin and Hassler, 7vansactions 
of the American Institute of Electrical Engineers, vol. ix., p. 271, 
1892. 

The Most Economical Age of Incandescent Lamps, by Carl 
Hering, zdzd@., vol. x., p. 65, 1893. 

Conductivity of Incandescent Carbon Filaments and of the Space 
Surrounding Them, by John W. Howell, zdzd., vol. xiv., p. 27, 
1897. 

The Incandescent Lamp (Manufacture), by Manning K. Eyre, 
The Electrical World, Jan. 5, 1895. 

Incandescent Lamps, by Francis W. Willcox, Journal of the 
Franklin Institute, April, 1900. 


LAMES NOL HUPLOYVING CARBON. 427 


GArieAs Rly EaRgexe vel: 
LAMPS NOT EMPLOYING CARBON. 


Av forms of electric lamp in successful use prior to 1900 
employed carbon as the light-giving body. This applies to are 
lamps, which in all cases are provided with carbon electrodes, and 
to incandescent lamps, which employ carbon filaments. There 
are, however, two other interesting classes of lamps which do not 
use carbon: one includes the so-called vacuum tubes, in which all 
the light is emitted by a gas or vapor; and the other comprises 
incandescent lamps, in which the filament is composed of some 
material other than carbon, the ernst lamp being a prominent 
example. The use of vacuum tubes as sources of light is a very 
old idea, being described by Hauksbee in a treatise published 
about two hundred years ago.* He employed glass vessels con- 
taining rarefied air, made luminous by frictional electricity, and to 
quote his own words, the light was “so great that large print, 
without much difficulty, could be read by it.”’ 

Similar, but not much more successful, attempts have been 
made repeatedly during the succeeding two centuries. The devel- 
opment of the Geissler and other improved forms of vacuum 
tube, and of the induction coil, during the past fifty years or more, 
has facilitated and encouraged such investigations. 

Mr. Nikola Tesla, in a paper on “Experiments with Alternate 
Currents of Very High Frequency and Their Application to 
Methods of Artificial [lumination,’ + gave prominence to this 
subject, and has since’ investigated and written further in con- 
nection with it, but has not yet advanced beyond the experimental 
stage. A paper on “Recent Developments in Vacuum Tube 
Lighting,” { by Mr. D. McFarlan Moore, describes the methods 

* Physico mechanical Experiments, etc., London, 1709. 
+ Transact. Amer, Inst. Elec. Eng., vol. viii., p. 267, May, 1891. 
t J/édzd., vol. xiii., p. 85, April, 1896. 


‘ 


428 ELECTRIGSLIGH GING. 


employed and results obtained by him. In his laboratory and at 
the New York Electrical Exhibition of 1896 he showed a room 
of considerable size lighted fairly well in this way, but no com- 
mercial applications have yet been made. In another series of | 
investigations, Mr. Cooper Hewitt of New York City has suc- 
ceeded in making a vacuum tube lamp of several hundred candle- 
power, and having a very high efficiency of about 4 watt per candle- 
power ; but these very promising results have not been published, 
and his methods up to the present time have not been applied 
commercially. | 

The chief advantages to be expected from vacuum tube lamps 
are high efficiency, long life, and distribution of light. The last 
is due to the large volume from which the light is given off; for 
example, a tube one foot long and an inch in diameter, or even 
larger, is lumincus throughout. In the ordinary incandescent 
lamp the light is emitted from a filament six to ten inches long 
and a few thousandths of an inch in diameter. This is practically 
a line, and produces too sharp an image upon the retina, as shown 
by the fact that it persists after the eye is shut or turned away 
from the light. 

The vacuum tube should have a long life, since the light- 
giving body being a gas, and not a solid, is not worn away. On 
the other hand, the degree of vacuum may rise or fall owing to 
absorption of the gas or leakage of air, in either case changing 
the resistance of the tube and interfering with constancy of action. 
The high efficiency of a vacuum tube results from the fact that a 
gas or vapor may be raised to a much higher temperature than 
a solid. The consequence is, the quantity of light emitted is 
increased in comparison with the emission of heat. In fact, such 
sources are often said to give “light without heat,” but in most 
cases heat is given off with the light. Nevertheless, it is true 
that a glow-worm, for example, or some phosphorescent body, 
radiates a large part of its energy within the visible spectrum, 
the proportion of the longer, non-visible waves, called radiant heat, 
being far less than with ordinary sources of light. 

There appears to be a discrepancy between the statements that 
the temperature in a vacuum tube is high, and yet the heat given 
off is small, but these are easily reconciled. If a 110-volt, 16 
candle-power lamp is supplied with about 125 volts, it will give 


LAMPS NOT EMPLOYING CARBON. 429 


32 candle-power. The power consumed is increased in about the 
ratio 110? : 125? = 12100 : 15625, or about 30 per cent, as shown 
on page 421. Hence the rate of the total emission of energy is 
raised 30 per cent, but the light emitted is doubled. Thus the 
quantity of heat for the same amount of light would be only 
130 + 2 = 65 per cent as great as before. By carrying this still 
further, the proportion of heat to light can be reduced very greatly, 
and what is called “light without heat’ may be produced. It is 
also a fact that the temperature of the filament is increased at the 
same time, but in order to give the same candle-power its mass 
may be diminished. This applies exactly toa vacuum tube lamp 
in which the mass is very small, but the temperature of the indi- 
- vidual particles is raised to a high point by the passage of electric 
current or discharge. It is possible that the electrical effect upon 
the atoms or ions may be somewhat different from what is ordi- 
narily called high temperature ; but it amounts to the same thing, 
since high rates of vibration or short wave lengths are produced. 

In the experiments of Tesla, luminous discharges were created 
in vacuum tubes or even in the open air by a high frequency 
generator (10,000 to 20,000 periods per second) connected to the 
primary of an induction coil, the secondary of which gave very 
high voltage. He also employed a form of induction coil in the 
primary of which electrical oscillations are set up by sudden 
breaking of the circuit, producing a much higher frequency 
(100,000 or more periods per second), and therefore giving an 
_ extremely high voltage with only a few turns of wire. In this 
way vacuum tubes were made to glow by holding them near the 
terminals, but without any electrical connection to them. Such 
forms of apparatus are hardly suitable for practical use, and they 
involve considerable losses from leakage. 

Moore employed induction tubes with connections made to 
them in the usual manner and operating at comparatively low 
voltage obtained from a self-induction coil with an electromagnetic 
make-and-break in the circuit. The latter was placed in a vacuum 
in order to give a sudden break and to avoid burning the contact 
points, but even with this precaution such a device is likely to give 
trouble. The Wehnheldt interrupter may be substituted, but it 
is doubtful if any form of break yet devised can be relied upon to 
act for the long periods of time demanded in lighting service. 


430 ELECTRIC LIGHTING. 


The tubes developed by Hewitt are of sufficiently low resist- 
ance to operate at ordinary pressures. They may be connected 
directly to the present 110-volt circuits without requiring any 
step-up transformer or make-and-break device, which is a great 
advantage from the practical standpoint. Unfortunately it requires 
about 1000 volts to start the discharge, after which it is maintained 
by 110 volts. 

The Nernst Lamp. — The type of lamp invented by Professor 
Nernst * of Géttingen, employs, in place of the long carbon fila- 
ment of the ordinary incandescent lamp, a shorter “strip of mate- 
rial which is an insulator at ordinary temperatures, but becomes a 
good conductor and luminant at high temperatures.’’ Usually it is 
composed of a mixture of metallic oxides, such as magnesia, yttria, 
zirconia, thoria, or ceria. Another feature of the Nernst lamp is 
the fact that the incandescent material is not burned by exposure 
to the air, consequently it need not be inclosed in a vacuum. 

Since the filament does not become a conductor until heated, 
some means must be provided to raise its temperature so that the 
current may flow through it. Two 
methods are employed, one consisting 
simply in applying the flame of a 
match or alcohol lamp directly to the 
filament after it is connected to the 
circuit. When its temperature is raised 
sufficiently the current passes through 
it, bringing it up to and maintaining 
it at a white heat. The other method 
is automatic, the current being passed 
through a spiral 4A which surrounds 
Fig. 378. Automatic Nernst Lamp. the filament / (Fig. 3878), and heats 

it until the current flows through it. 








This causes the magnet J/ in series with / to attract its arma- 
ture A and break contact with the screw P, thus disconnecting 
the heating spiral A H which is in parallel with the filament F. 
When the lamp is turned out by opening the circuit, the spring 
S brings the armature A back into contact with the screw P, and 
the automatic device is ready to act again. The heating device 
H{ff is of porcelain, which, before being baked, is wound with a 
* U.S. Patent No. 623,811, April 25, 1899, 


LAMPS NOT EMPLOYING CARBONS. 431 


great many turns of fine platinum wire. During the baking this 
wire becomes embedded in the porcelain, and is thus held firmly, 
only the outer surface being visible. The resistance # consists 
of iron wire placed in series with the filament F, so that the 
increase in resistance of the former compensates for the decreasing 
resistance of the latter, when the temperature rises. 

The non-automatic lamp is provided with an open globe to 
permit lighting by a match; and the automatic form is contained 
in a closed globe, but it need not be air-tight. These lamps may 
be connected in parallel to the ordinary 110 or 220 volt circuits,. 
and are claimed to have a high efficiency of 1.5 to 1.75 watts per 
candle-power, being one-half the power required by a carbon fila- 
ment giving the same light. On the other hand the hfe is shorter, 
the average being about 200 to 300 hours, after which the filament 
loses its strength and increases in resistance. This, however, is the 
only part that is used up, and may be readily renewed, since the 
lamp is not hermetically sealed. The light is whiter than that of 
ordinary incandescent lamps, and the filament being much shorter, + 
and giving 25, 50, or 100 candle-power, produces a dazzling effect 
on the eye unless a ground glass or equivalent globe- is used. At 
the Paris Exposition of 1900 the Allgemeine Elektricitats Gesell- 
schaft of Berlin exhibited a room brilliantly illuminated by Nernst 
lamps, being the first important public application. 


432 FLUE CTRICHTAGIOIING 


OE Agr at Rael Ne 
| METERS. 


THE general name meter may be applied to any device for 
measuring electrical quantities, and we have many forms of ampere- 
meter, voltmeter, wattmeter, etc. Ordinarily, however, the term 
meter or electric meter, unless combined with another word, means 
an instrument to vecord, register, or integrate current in ampere- 
hours or energy in watt-hours. They are commonly used in 
stations or in the service connections of the various consumers to 
take account of the amount of current or energy supplied. 

Classification of Meters. — Various electrical effects have been 
utilized in connection with meters, and the latter may be classified 
from that point of view, as follows : 


Principle of action. Example. 
Electrochemical effects. . . Edison meter. 
Electrical heating effects. . . Forbes meter. 
Electromagnetic effects . . American (Marks) meter. 
Electrodynamic effects. . . Thomson meter. 
Alternating current effects . Shallenberger meter. 


Qualities Required in Meters. — Few devices are called upon 
to fulfill so many and such difficult conditions as those under 
which an electric meter is likely to work. For this reason its de- 
velopment has been one of the most serious problems that elec- 
trical engineers have had to solve. The chief qualities that are 
required or desired in meters are the following : 

1. Accuracy. Under any reasonable conditions a meter should 
be at least commercially accurate, that is, its errors should not ex- 
ceed 2 or 8 per cent. ; | 

2. Range. A meter should measure with commercial accu- 
racy for any load from the maximum down to the smallest 
that may exist. This is probably the most difficult condition 


METERS. yey 


to meet. For example, a meter that will record correctly for 
100 lamps is not generally capable of acting at all when only 
one lamp is burning. Even if it takes some account of a single 
lamp, the record would be very inaccurate. To be sure, a certain 
percentage of error with a few lamps is less serious than for many, 
but it often happens that a small number may burn nearly all 
the time, in which case the aggregate error becomes large. 

3. Consumption of Energy. Practically all forms of meter 
consume some energy,.and if this loss goes on continually in a 
great many of them it may amount to a large item in the course 
of a year. Hence a meter should waste less than one per cent of 
the energy that it measures, and this loss should decrease some- 
what in proportion to the load, which is usually the case. 

4. Drop in Voltage. Besides the mere consumption of power, 
it is even more objectionable to have a drop in voltage on a con- 
stant potential system, especially for incandescent lighting. — If 
the current C passes through any resistance R a drop C R is pro- 
duced, hence the resistance introduced into the circuit by the 
meter should be as small as possible, so that the drop at full load 
shall not exceed + per cent of the working voltage. In a watt- 
meter the series resistance produces such a drop as well as loss of 
energy, but the shunt coil merely uses a very small portion of the 
current, which is less objectionable. 

0. Durability. It is very important that none of the parts 
should be likely to wear rapidly or get out of order. 

6. Aztentzon. The care and attention required should be small, 
and frequent inspection or testing unnecessary. 

1. Registration. The meter should record or register in a 
clear manner, so that the consumer can read it at any time and 
check its accuracy. 

8. Testing. It should be an easy matter to test the meter 
and verify it. : 

9. Cheating. The meter should be so constructed and pro- 
tected that it is not liable to be tampered with in order to change 
its reading. 

10. Cost. The price should be sufficiently low, so that a large 
deposit or rental need not be charged. 

11. Alternating and Direct Currents. It is desirable that a 
meter may be used for either kind of current; but it is generally 


434 ELECTRIC LACH TING: 


bought for one or the other, and this point is not so very impor- 
tant. 

12. Frequency. It is desirable also that -variatiors in fre- 
quency should have no effect ; but the latter being fixed in most 
cases, it is sufficient to adjust for it in the first place. 

13. Portability. A meter should be strong enough so with 
moderate care it may be carried about without injury. 

It cannot be expected that any meter will fulfill all of the 
above conditions, but there are several types in use which do so 
reasonably well. 

Methods of Charging for Electrical Energy. — If the demand 
upon an electrical generating plant were uniform at all times, a 
simple charge of a certain rate per k. w. hour would be sufficient, 
possibly giving the larger consumers a lower rate, as is customary 
in other branches of business. In electric lighting, however, the 
demand varies widely at different hours of the day and night, 
which introduces serious difficulties in technical as well as business 
management. For example, the load between 5 and 6 P.M. in 
winter may be many times the average load. It is customary to 
call the ratio of the average load to the maximum the “ load factor.” 
This is often as low as 10% and is rarely higher than 25 % 
in ‘electric. lighting.s ~The (use of senersy for motors, heatersmecies 
tends to make the demand more uniform, and therefore raises the 
load factor. It is evident that the capacity of machinery, etc., in 
an electric lighting plant must be somewhat greater than the 
maximum demand, in order to give a margin in case of break- 
down of part of the apparatus. Hence an increase in the load at 
its maximum point requires a corresponding increase in capacity. 
On the other hand, the demand upon the system during hours in 
the day when the load is light can be taken care of without any 
increase in plant. In other words the station can afford to sell 
energy at a much lower rate during those hours. A striking 
illustration of the importance of this point is the fact that about 
one-quarter of the generating machinery in electric lighting 
stations is used only 50 to 100 hours per year, and may be prac- 
tically idle during all the rest of the time. These hours are 
usually between 5 and 7 p.m. during December and January. 
It is quite evident that this machinery cannot possibly earn its 
interest and depreciation charge durings these few hours at ordi- 


METERS. 435 


nary rates. It is necessary, however, to install it in order that 
the business may be held for the rest of the year. Various 
attempts have been made to take account of these points in 
charging for energy, and also to encourage its use at those hours 
when it can be delivered more economically. The several plans 
for selling electrical energy, some of which take account of these 
conditions, are as follows : — 


METHODS OF CHARGING FOR ELECTRICAL ENERGY. 


Ist, Contract to supply a certain number of lamps at a fixed price per month, 
whether they are used or not. 

2d, Meter with “ flat” (i.e., uniform) rate. 

3d, Meter taking account of maximum demand. 

4th, Meter, with two or more rates of charge for different periods of the day. 

oth, /ixed charge for energy plus a graded charge for the maximum capacity. 

6th, Prepayment meter, which only allows energy to be delivered for a certain 
coin deposited. 


The contract system of charging a fixed amount for a certain 
number of lamps was commonly adopted in the early days of 
electric lighting, except in Edison systems using the chemical 
meter. For street lighting, and other service requiring lights for 
a definite time, this system is satisfactory, but for residence light- 
ing it is quite unsatisfactory, because the consumer is likely to burn 
the lamps for the full time when they are not needed. This wastes 
a large amount of energy, which must ultimately be paid for by the 
users. In such cases, and in fact for general use, some form of 
meter should be adopted. The common plan is to charge a cer- 
tain price per lamp-hour or k. w. hour, which is’ graded according 
to the amount used. For example, a common practice is to 
charge one cent -per lamp-hour, if the consumption is equivalent 
to the full number of lamps burning for one hour per day; 4 cent 
if equivalent to two hours, and so on. This accomplishes its pur- 
pose fairly well, but fails, however, to take into account the par- 
ticular time at which the lamps are burned. The latter point may 
be covered by using a two-rate meter, which separates the energy 
consumed during certain hours from that used during the rest of 
the time, a higher rate being charged for the former. One way 
of accomplishing this is to use two separate meters which are 
switched in or out of the circuit by clock-work. Another plan is 
to cause the meter to run faster during the time that a higher 


436 ELECTERICALICLHIING: 


charge is to be made, thus arriving at the same result. The 
prepayment meter is not intended to accomplish any of these 
ends, but is simply to avoid the necessity for giving credit. 

The arbitrary method of charging a certain price per unit for 
one quantity, and 4 as much for a greater quantity, is objection- 
able, because it leads to the absurd result that one may reduce the 
amount of his bill by using a little more current. The sliding- 
scale, in which the reduction is a certain percentage of the amount 
used, would avoid this difficulty. It might not be quite so easily 
understood as a certain price per lamp-hour, but customers would 
soon understand this plan. It would seem to be practically im- 
possible to make a perfectly fair arrangement between producers 
and consumers; but a reasonable approximation can be reached, 
which is close enough for ordinary business purposes. 
| The Edison Chemical Meter was the first successful type, and 
many thousands of them were in regular and satisfactory service 
fora number of years. For reasons, given later, they have been 
replaced by other forms operating mechanically. In principle, this 
meter is based upon Faraday’s law, according to which the amount 
of electrochemical action, for example, the weight of metal de- 
posited or dissolved in an electrolytic cell, 1s directly proportional 
to the current, the chemical equivalent, and the time. The 
ampere, as legalized in all important countries, being defined in 
terms of the weight of silver deposited, this principle is funda- 
mentally correct. For reasons of cheapness and as a result of 
numerous experiments, Edison adopted zinc as the best metal for 
the purpose. 

The meter consists of a cell C, containing a solution of zinc 
sulphate having a density of 1.11, in which two zinc electrodes, 
A and 2B, are immersed. These are kept parallel’ and at a fixed 
distance apart by hard-rubber bolts. Connection is made to them 
by copper rods inserted in their upper ends, as indicated. In one 
of the main conductors, + or — which supply the lamps Z, whose 
current is to be measured, a german-silver shunt S is introduced, 
having a certain resistance that is practically constant for ordinary 
‘temperature changes. 

The electrolyte in the cell has a certain resistance, which 
decreases with rise of temperature ; and in series with it is a coil 
R of copper wire whose resistance increases with temperature, the 


METERS. A3T 


two being proportioned so that they compensate each other and 
keep the resistance of the cell circuit almost perfectly constant for 
ordinary changes in temperature, The resistance of the coil & is 
about 4 times that of the bottle, and the two together have many 
times the resistance of the shunt S, so that a certain small fraction 
of the total current passes through the cell, dissolving zinc from the 
anode A and depositing it upon the cathode C. Once each 
month the electrodes are removed from the cell, being replaced by 
others, and. the loss in weight of the anode is carefully weighed 
by a chemical balance. This loss in grams multiplied by the ratio 
of resistances of the two branches of the circuit and divided by 
.000337, the electrochemical equivalent of zinc, gives the total 
number of ampere-seconds during the month. 

The possible sources of error are due to temperature changes, 
which are almost perfectly compensated in the cell circuit as 
already explained, and only vary the 
Shunbes anoutmeiperecentstor. 15°C 
above or below the normal. The cell + 
has a certain counter E.M.F. of .001 
to .003 volt, which introduces an error 
at loads less than 3 per cent of the 
maximum. Oxzzdation of the plates © 
also occurs and is allowed for, other- 
wise the loss in weight would appear i, 379. Edison Chemical Meter. 
too low. The drop produced in the 
- main circuit is small even at full load, being only about 4 %. 

With reasonable care this meter is fairly accurate; but the 
trouble of collecting and weighing the plates, and the fact that the 
consumer cannot read the record himself, has lead to the substi- 


— 





tution of more convenient forms. 

Thomson Recording Wattmeter.— This type, developed by 
Professor Elihu Thomson, and used in very large numbers in this 
country and abroad, is essentially an electric motor. The general 
appearance of the standard two-wire form for direct or alternating 
currents is shown in Fig. 380, and the connections in Fig. 381. 
The field magnet of the motor consists of two stationary coils of’ 
heavy wire directly in series with one of the main supply con- 
ductors, so that the entire current to be measured passes through 
them. An armature provided with a winding of many turns of 


438 ELECTRIC LIGHTING. 


fine wire and having a resistance in series with it is connected 
across the circuit between the main conductors, and is mounted 
to rotate on a vertical axis between the two field coils. The 
armature 1s equipped with a miniature silver commutator and with 
brushes similar to those of a direct current motor, but, like the 
field coils, does not contain any iron core. Since the magnetic 
circuit passes through air and other non-magnetic materials, the 
flux through the armature, though small, is directly proportional 
to the main current. The armature circuit having a constant high 





Fig. 380. Thomson Recording Wattmeter. 


resistance connected across the two supply conductors, takes a 
current exactly proportional to the voltage between them. Hence 
the torque of the motor is in proportion to the product of 
these two currents or to the number of watts supplied at any 
instant. A copper disc mounted upon the shaft of the motor 
revolves between the poles of permanent magnets, as shown in 
Fig. 380, and acts as a brake, owing to the Foucault currents 
generated in it. These currents being directly proportional to 
the speed, the armature will rotate twice as fast with twice the 


METERS. 439 


torque; consequently the revolutions per minute are directly pro- 
portional to the power supplied in watts. The total number of 
revolutions in any given time represents the energy in watt-hours. 
A train of wheels operates a series of five dials representing 
1,111,100 units, usually watt-hours, and readings taken _periodi- 
cally show the energy consumed during the intervals. 

It is evident that a motor meter requires a certain current to 
overcome friction, and would fail to record any current below this 
limit. In order to overcome this difficulty, an auxiliary field coil 
of fine wire marked “shunt” in Fig. 381 is put in series with the 
armature. Since the latter is connected across the main con- 
ductors, the current through it depends solely upon the voltage 
whether any lamps are burning or not. The resistance of the 
armature circuit 1s so adjusted that this current passing also 
through the shunt coil develops a 
torque almost sufficient to over- 
come friction; hence any current 
flowing in the main circuit and 
field coils will produce its full 
effect in rotating the armature. 
If the armature current is too 
strong it will cause slow rotation, 





even when no lamps are burning, 


Fig. 381. Connections of Two-wire Meter. 


and this ‘creeping’ should be 
stopped by reducing the number of turns in the shunt field coil 
until the armature is not quite able to turn when no current for 
lighting or other purposes is being used. 

The accuracy of the meter also requires that a certain number 
of watts supplied shall produce the proper number of revolutions 
per minute. Ordinarily 60 watts should cause the armature to 
rotate once per minute, and so on for other loads. Measuring 
the power with a wattmeter, or putting on a known load of lamps, 
enables the accuracy of the meter to be tested by counting the 
revolutions per minute. If found incorrect, the speed may be 
Jowered by setting the permanent magnets farther out, or vice 
versa, an adjustment of about 16% being possible. Since a 
reversal of current in both field and armature of a motor does 
not change the direction of rotation, an alternating current may 
be measured by this same instrument. The absence of iron cores 


440 ELECTRIC LIGHTING. 


avoids any troubles from hysteresis or eddy current; but it is 
necessary that the reactance of the armature circuit should be 
very small compared with its resistance, a condition which is 
fulfilled by inserting resistance, as explained in relation to Fig. 381. 
A lag in the main current due to the load itself, as in the case of 
arc lamps or motors, does not introduce any error, since the 
instrument properly measures and integrates the true energy in 
watt-hours. 

Special Forms of Thomson Meter are made for various pur- 
poses. The type whose connections are shown in Fig. 882 is 
designed for direct or alternating current three-wire circuits. In 
this case one main field coil is connected in series with each of 
the outer conductors, the armature circuit, including the shunt 
field, being connected between the neutral and one of the outer 


Generator 





Fig. 382. Thomson Three-wire Meter. Fig. 383. Meter for Large Currents. 


conductors, assuming that the two sides of the system are per- 
fectly balanced. . It may also be connected across both sides, thus 
measuring the total voltage; but the armature will then rotate 
twice as rapidly, for which fact adjustment or allowance should be 
made. The currents on either or both sides of the system pro- 
duce their full effect in the main field coils. ' 

The meters already described may be used for secondary or 
other low-voltage alternating circuits, but for primary or high- 
voltage circuits a modified form is applicable. The modification 
consists in inserting a small meter-transformer, which reduces the 
high voltage to a moderate value proportional to the original, the 
instrument being calibrated accordingly. 

For measuring very large direct or alternating currents, as in 
generating plants, the field magnetism is produced by a single 


METERS. 441 


bar of copper which passes between two armatures, as represented 
in 383, the arrangement in other respects being similar to that 
already described. 

Two or three phase currents may be measured by means of 
a separate meter connected in each phase. If the energy of the 
two or three phases is kept balanced, one meter in one phase is 
sufficient, its readings being multiplied by two or three as the 
case may be. For unbalanced circuits the two or three separate 
instruments may be combined in one, as illustrated in Fig. 384. 





Fig. 884. Thomson Polyphase Meter. 


A single instrument of this kind is capable of recording cor- 
rectly the total load on balanced or unbalanced two-phase, three- 
phase, or monocyclic circuits, and saves space, expense, as well as 
the trouble of reading, and keeping account of two or more 
sets of dials. In many cases, however, separate meters are em- 
ployed for the different phases of current. The arrangement for 
unbalanced three-phase or monocyclic circuits is shown in Fig. 
385. One meter is connected to one branch of the circuit, and a 
second to another branch ; but none is required in the third branch, 
since no current can flow in it without passing through one or 
both of the other branches. The algebraic sum of the readings 


442, BELECTRICRLIGCH LING. 


of the two instruments gives the total power and is independent 
of the balance or lag of the currents. If the latter is less than 
60°, giving a power factor greater than .50, the arithmetical sum 
of the readings is taken; but with a lag greater than 60°, the 
relation between the currents in the series and shunt coils of one 


CONNECTIONS OF 
THOMSON RECORDING WATT-METER 
UNBALANCED THREE-PHASE CIRCUITS 
OR MONOCYCLIC SECONDARY CIRCUITS 


S TO ISO AMPERES 


t 
if 
' 
‘0 
' 
H 
i 
' 
HL 
' 


Resistance Q) Resistance 


Line 
In monocyclic circuit this is the 
common connection of the transformers. 


Line 





fig. 385. Polyphase Cireuit with Two Meters. 


of the wattmeters causes it to have a negative reading, hence the 
difference between the two readings is equal to the actual power. 
In electric lighting the power factor is always greater than .50, 
and even with motors on the circuit it should be kept above that 
value. This arrangement is adapted to secondary or other low- 
voltage circuits ; for primary or other high-voltage circuits, the 


METERS. 


445 


connections are similar, except that the pressure is reduced by 
meter-transformers as already explained. 


For three-phase circuits with 
Y connection (p. 144), three sep- 
arate meters may be used, one in 
each branch, but the single or 
the two-instrument arrangements 
are generally preferred. 

Sertes or Arc-Circuit Meter. 
— The Thomson instrument is 
adapted also to constant current 
circuits for series arc or incan- 
descent lighting, the connections 





Fig. 386. Series Circuit Meter. 


being represented in Fig. 386. The field coils of coarse wire are 





Fig. 387. Shallenberger Meter. 





connected in series with 
one main conductor carry- 
meethe winllicurrent,. the 
same as for constant po- 
tential circuits. In this 
Case, however, 7a’) cut-out 
is provided which short- 
circuits, the lines at =that 
point in case. the circuit is 
opened beyond. The cut- 
out magnet is operated by 
coils in series with a high 
resistance and connected 
across the line wires. The 
armature 1s shunted across 
a portion of this resistance, 
as shown, and therefore re- 
ceives a certain small frac- 
tion of the line voltage, so 
that with proper calibra- 
tion the meter registers the 
watt-hours consumed in 
that portion of the circuit. 


The Shallenberger Meter illustrated in Fig. 387 is a promt- 
nent form, having been made for many years by the Westinghouse 


444 ELECTRIC LIGHTING. 


Company. It is of the motor type, but is applicable only to alter- 
nating currents and records ampere-hours but not watt-hours. It 
consists of large fixed coil having a few turns of heavy wire through 
which passes the entire current to be measured. Inside of this, 
and at an angle to it, is placed a closed copper coil. Within the 
latter a thin metallic disc is mounted to rotate upon a vertical 
spindle connected at its upper end with a train of recording gears 
and equipped below with four aluminium fan blades. When an 
alternating current passes through the large coil, it acts as a 
primary, and induces a current in the closed or secondary coil. 
The magnetic field produced by the secondary is at an angle to 

that of the primary, and 
the two combine to form 
a resultant field; but as. 
their alternations do not 
coincide in time the direc- 
tion of this resultant is 
continually shifting and 
produces a rotating field,. 
as explained on page 145. 
The metallic disk tends to. 
rotate in unison with the 
field, but is retarded by 
the fan blades. “This de- 
vice being in principle 





an induction motor, its. 
torque increases as the 


Fig. 388. 


square of the primary current; but since the resistance to rotation 
rises as the square of the speed (at moderate values), the number 
of revolutions per minute are directly proportional to the current, 
which is the condition required. 

The Westinghouse Integrating Wattmeter (Fig. 388) is also of 
the induction motor type, but differs from the Shallenberger instru- 
ment, in having in addition to the series coils a shunt winding, the 
effect of which is proportional to the voltage, so that watt-hours. 
are recorded. Since a rotating aluminium disk is acted upon by 
induction, it can be used only with alternating currents. . The 
moving parts being very light require only 1.25 watts in the shunt 
winding, and even less in the series coils. The former advantage 


METERS. 445 


is important because that loss occurs all the time, even when lamps 
are not burning, and any drop in the series coil is equally objection- 
able, since it reduces the pressure at the lamps. For 400 volts or 
less and currents up to 80 amperes, the meter is connected directly 





Fig. 389. Connections for Two-phase Westinghouse Meters. 


tothe circuit. With higher voltages or heavier currents a potential 
transformer is used to reduce the pressure for the shunt winding, 
and a series transformer is inserted in one of the main conductors 
to obtain a smaller but proportionate current for the series coil. 
The connections for a two-phase circuit are shown in Fig. 389, a 


446 ELECTRIG\LIGHTING. 


potential transformer for each phase being placed below and a 
smaller series transformer for each phase above, with ail four 
secondary wires leading to a single meter in the center. The 
energy is brought from two-phase generators by four wires from 
the right, and after being measured is carried to the lamps by four 
wires on the left. The dials record the total energy supplied in 
all the branches of a polyphase circuit into which the wattmeter 
is connected, no multiplier being necessary. 

The Duncan Integrating Wattmeter, represented in Fig. 390, is 
another well-known form of 
the induction motor type 
for alternating currents 
only. It comprises a series 
field core of laminated iron 
with inwardly projecting 
poles carrying the series 
coils, between which the 
armature — an inverted 
aluminium cup — rotates 
upon a vertical spindle, as 
shown. The shunt coil 
placed inside of the arma- 
ture, with its axis at right 
angles to that of the series 
coils, is also wound upon a 
laminated iron core, being 
stationary and supported 
from below by a brass arm. 
The upper end of the arm- 
ature spindle carries a gear 
driving the train of dials, 
and on the lower end is mounted the retarding disk of aluminium 
which revolves between the poles of two permanent magnets. 
The so-called compensator is a copper ring with an iron core 
shown in front of the armature and supported by a movable arm. 
By adjusting its position, friction may be overcome and at the 
same time “creeping” avoided. The lower bearing of the spindle 
is of sapphire and the spindle point of hardened steel, both of 
which are easily renewable. 





Fig. 390. Duncan Meter. 


METERS. AAT 


The Gutmann Integrating Wattmeter is similar in principle to 
the Westinghouse and Duncan instruments, being of the induction 
motor type with series and shunt windings, and is adapted only to 
alternating currents. The arrangement of the dials, retarding 
disk and other parts is also similar, but the armature or rotating 
member is a diagonally slotted aluminium cylinder. 

The American Integrating Amperemeter, illustrated in Fig. 391, 
differs radically from those already described, both in principle 
and in construction. It consists of a solenoid and core placed 
above aself-starting pendulum, actuated by the electric current. 
The pendulum, by means of a cam, raises a pawl on a ratchet 





Fig. 891. The American Integrating Amperemeter. 


wheel to a uniform height each stroke. The solenoid, by means 
of its core, shifts the angular position of a pendent arch attached — 
to its axIs so as to permit this pawl to drop along the ratchet 
wheel a number of teeth proportional to the current passing 
through the meter; thus at each stroke of the pendulum the load 
in amperes passing to the consumer is, by means of the ratchet 
wheel and the counter register, measured and added up in ampere- 
hours. 

The pendulum ceases to swing when no lamps are burning ; but 
as soon as any are turned on, and current flows in the main con- 
ductor, the pendulum is started automatically, being actuated by a 


A4S ELECTRICOGIGH TING 


shunt circuit across the mains. The form illustrated is for use on 
a three-wire system, both of the outer conductors being carried 
through the solenoid, as indicated, so that its action upon the core, 
and therefore the position of the latter, depends upon the com- 
bined effects of the two currents, thus measuring the total load 
on both sides of the system. The core of soft iron is magnetized 
to saturation by a winding in circuit with the coil that drives the 
pendulum, the object being to avoid variations due to hysteresis. 
Having this construction, the instrument measures ampere-hours 
simply, since ordinary changes in voltage would produce no ap- 
preciable effect. 

The Ferranti Meter used in England is based upon the princi- 
ple that a conductor carrying a current in a magnetic field tends 
to move in a direction perpendicular to the current and to the 
lines of force. In this case the conductor consists of mercury con- 
tained in a shallow circular chamber placed between the poles of a 
magnet excited by a coil through which the main current passes. 
This current also flows radially through the mercury being intro- 
duced at the center by a pin, and taken off at the periphery by 
a metallic rim. The retarding force is that due to fluid friction 
of the mercury against the inner surface of the chamber, in 
which radial grooves are formed to increase the effect and make 
it as nearly as possible proportional to the square of the speed. 
Since the current flows in both the magnet and the mercury, the 
driving force 1s proportional to the square of the current, and 
the speed, therefore, increases directly with the current. A vane 
dipping in the mercury transmits the motion of the latter to the 
counting dials by means of'a small spindle. The driving force 
due to residual magnetism is designed to overcome the retarding 
force due to the solid friction of the-parts. . It 1s evident that this 
instrument measures ampere-hours and not watt-hours. 

The Aron Meter consisted originally -of an ordinary clock 
having a permanent magnet for the bob of the pendulum, below 
which was placed a coil with its axis vertical. The current to be 
measured passed through the coil-in the direction to repell the 
magnet, thus neutralizing a part of its gravity which caused the 
clock to lose time. The loss of time in any period enabled the 
ampere-hours during that period to be determined. A later form 
comprised two separate clocks, one acting normally and the other 


METERS. 449 


being influenced by the current. The two trains of wheels were 
connected by a differential gear to a third train with dials and 
pointers which indicated the difference in action of the two clocks, 
being calibrated in ampere-hours. This type involves two obvious 
difficulties : one 1s the trouble of winding the clocks, and the other 
is the practical impossibility of keeping correct a large number of 
clocks of reasonable cost. “These objections are overcome in a 
still more recent form which is made self-winding by the action of 
the current, and each pendulum is acted upon by a coil so that one 
is accelerated and the other retarded, thus doubling the effect. 
Furthermore, at frequent intervals the connections of the coils are 
reversed, so that first one and then the other pendulum is the 
faster, the difference between the two being always registered on 
the dials. In this way even a considerable deviation from accuracy 
in one or both of the clocks is eliminated by the constant reversal . 
of their relations. Another feature in the improved Aron instru- 
ment is the substitution of a shunt coil for the permanent magnet 
on each pendulum, thus converting it into an integrating watt- 
meter. It is adapted to either direct or alternating currents, and 
is made in forms suitable for two-wire, three-wire, and other 
circuits. 

Lhe Terms [ntegrating, Recording, and Registering Meter are 
all used for designating the various devices described in this chap- 
ter. The first is certainly correct, since in most cases the instru- 
ment merely integrates or sums up the total number of ampere- or 
watt-hours, without making any record of the almost constant vari- 
ations in load which usually occur. There are also instruments 
commonly called recording volt-, ampere-, or wattmeters, in which 
a line is traced out on paper showing the number of volts, etc., at 
any time during the entire twenty-four hours. By using an am- 
pere- or wattmeter of this kind and properly integrating the record 
obtained, the number of ampere- or watt-hours may be determined. 
This is much less convenient, however, than an instrument which 
automatically performs the integration and gives the result on a 
dial. On the other hand, the maximum demand and other values 
would all be shown, so that a charge could be made taking them 
into account, as explained in the beginning of this chapter. Asa 
matter of fact, such instruments are rarely used except to ascertain 
the uniformity of voltage, etc., when it is desired to have it con- 


450 ELECTRIC LIGHTING 


stant, and are used merely as a check on the regulation. It has 
been proposed to distinguish between this class and those which 
integrate, by calling the former recording and the latter register- 
ing; but common usage is the other way, and the term integrating 
meter is more distinctive for the latter. In most cases the simple 


y 


word “meter” is understood to mean the integrating instrument, 


whether used for measuring gas, water, or electrical quantities. 


JaNel ed vod SND 





“NATIONAL ELECTRICAL CODE” 





RULES AND REQUIREMENTS 


OF THE 


NATIONAL BOARD of FIRE UNDERWRITERS 


FOR THE INSTALLATION OF 


WIRING AND APPARATUS 
BORBEEEG ERI GUMIGHIASHEAT, AND ROWER 


AS RECOMMENDED BY THE 
UNDERWRITERS’ NATIONAL ELECTRIC ASSOCIATION 


EDITION OF 1o01 


The National Electrical Code, as it is here presented, is the result of the 
united efforts of the various Electrical, Insurance, Architectural, and allied 
interests which have, through the Nationa) Conference on Standard Electrical 
Rules, composed of delegates from various National Associations, unanimously 
voted to recommend it-to their respective Associations for approval or adoption. 

The following is a list of the Associations represented in the Conference, 
all of which have approved of the Code: 

AMERICAN INSTITUTE OF ARCHITECTS 

AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS 
AMERICAN SocIETY OF MECHANICAL ENGINEERS 
AMERICAN STREET RAILWAY ASSOCIA TION 
Facrory Mutua Fire INSURANCE COMPANIES 
Nationa ASSOCIATION OF FIRE ENGINEERS 
NATIONAL BOARD OF FIRE UNDERWRITERS 


NaTIONAL Evectric Light ASSOCIATION 
UNDERWRITERS’ NATIONAL ELECTRIC ASSOCIATION 


GENERAL PLAN GOVERNING THE ARRANGEMENT OF RULES 


CLASS A.—Central Stations, Dynamo, Motor, and Storage-Battery Rooms, 
Transformer Substations, etc. Rules 1 torr. 
CLASS B.— Outside Work, all systems and voltages. Rules 12 and 13. 


451 


452 ELECTRIC LIGHTING. 


CLASS C.—Inside Work. Rules 14 to 39. Subdivided as follows: 
General Rules, applying to all systems and voltages. Rules 14 to 17. 
Constant-Current systems. Rules 18 to 20. 
Constant-Potential systems. 
All voltages. Rules 21 to 23. 
Voltage not over 550. Rules 24 to 31. 
Voltage between 550 and 3,500. Rules 32 to 37. 
Voltage over 3,500. Rules 38 and 39. 


CLASS D.— Specifications for Wires and Fittings. Rules 40 to 62. 
CLASS E.—Miscellaneous. Rules 64 to 67. 
CLASS F. — Marine Wiring. Rules 68 to 80. 


CLiass A 
STATIONS AND DYNAMO ROOMS 


INCLUDES CENTRAL STATIONS, DYNAMO, MOTOR, AND STORAGE-BATTERY ROOMS, 


TRANSFORMER SUBSTATIONS, ETC. 
1. Generators — 


a. Must be located in a dry place. 

6. Must never be placed in a room where any hazardous process is carried 
on, nor in places where they would be exposed to inflammable gases or flyings 
of combustible materials. 

c. Must be insulated on floors or base frames, which must be kept filled 
to prevent absorption of moisture, and also kept clean and dry. Where frame 
insulation is impracticable, the Inspection Department having jurisdiction 
may, in writing, permit its omission, in which case the frame must be per- 
manently and effectively grounded. 


A high-potential machine which, on account of great weight or for other reasons, cannot have its 
frame insulated from the ground, should be surrounded with an insulated platform. This may be made 
of wood, mounted on insulating supports, and so arranged that a man must always stand upon it in 
order to touch any part of the machine. 

In case of a machine having an insulated frame, if there is trouble from static electricity due to 
belt friction, it should be overcome by placing near the belt a metallic comb connected with the earth, or 
by grounding the frame through a very high resistance of not less than 200 ohms per volt generated by 
the machine. 

ad. Every constant-potential generator must be protected from excessive 
current by a safety fuse, or equivalent device, of approved design in each lead 
wire. 

These devices should be placed on the machine or as near it as possible. 

Where the needs of the service make these devices impracticable, the Inspection Department 
having jurisdiction may, in writing, modify the requirements. 

e. Must each be provided with a waterproof cover. 

J. Must each be provided with a name-plate, giving the maker’s name, 
the capacity in volts and amperes, and the normal speed in revolutions per 
minute. 

2. Conductors — 


v 


From generators to switchboards, rheostats, or other instruments, and 
thence to outside lines. 


APPENDIX I. 453 


a. Must be in plain sight or readily accessible. 

6. Must have an approved insulating covering as called for by rules in 
Class “C” for similar work, except that in central stations, on exposed 
circuits, the wire which is used must have a heavy braided non-combustible 
outer covering. 

Bus bars may be made of bare metal. 

c. Must be kept so rigidly in place that they cannot come in contact. 

ad. Must in all other respects be installed under the same precautions as 
required by rules in Class “C” for wires carrying a current of the same volume 
and potential. 


3. Switchboards — 


a. Must be so placed as to reduce to a minimum the danger of communi- 
cating fire to adjacent combustible material. 


Special attention is called to the fact that switchboards should not be built down to the floor, nor 
up to the ceiling, but a space of at least ten or twelve inches should be left between the floor and the 
board, and from eighteen to twenty-four inches between the ceiling and the board in order to prevent fire 
from communicating from the switchboard to the floor or ceiling, and also to prevent the forming of a 
partially concealed space very liable to be used for storage of rubbish and oily waste. 


6. Must be made of non-combustible material or of hardwood in skeleton 
form filled to prevent absorption of moisture. 

c. Must be accessible from all sides when the connections are on the back, 
but may be placed against a brick or stone wall when the wiring is entirely on 
the face. 

a. Must be kept free from moisture. 

-e. Bus bars must be equipped in accordance with rules for placing 
conductors. 


4. Resistance Boxes and Equalizers — 


(Lor construction rules, see Vo, 60.) 
a. Must be placed on a switchboard or, if not thereon, at a distance of a 
a foot from combustible material, or separated therefrom by a non-inflammable, 
‘non-absorptive, insulating material. 


5. Lightning Arresters — 
(For construction rules, see No. 63.) 


a. Must be attached to each side of every overhead circuit connected with 
the station. 


It is recommended to all electric light and power companies that arresters be connected at intervals 
over systems in such numbers and so located as to prevent ordinary discharges entering (over the wires) 
‘buildings connected to the lines. 


6. Must be located in readily accessible places away from combustible 
materials, and as near as practicable to the point where the wires enter the 
building. 

Station arresters should generally be placed in plain sight on the switch- 
board. 

In all cases, kinks, coils, and sharp bends in the wires between the arresters 
and the outdoor lines must be avoided as far as possible. 


454 ELECTRICCLIGHI ING: 


c. Must be connected with a thoroughly good and permanent ground con- 
nection by metallic strips or wires having a conductivity not less than that of a 
No. 6 B. & S. copper wire, which must be run as nearly in a straight line as 
possible from the arresters to the earth connection. 

Ground wires for lightning arresters must not be attached to gas-pipes 
within the buildings. 


It is often desirable to introduce a choke coil in circuit between the arresters and the dynamo. In 
no case should the ground wire from a lightning arrester be put into iron pipes, as these would tend to 
impede the discharge. 


6. Care and Attendance — 
a. A competent man must be kept on duty where generators are operating. 
6. Oily waste must be kept in approved metal cans and removed daily. 


Approved waste cans shall be made of metal, with legs raising can three inches from the floor, and 
with self-closing covers. 


7. Testing of Insulation Resistance — 


a. All circuits, except such as are permanently grounded in accordance 
with Rule 13 A, must be provided with reliable ground detectors. Detectors 
which indicate continuously, and give an instant and permanent indication of 
a ground, are preferable. Ground wires from detectors must not be attached 
to gas-pipes within the building. 

6. Where continuously indicating detectors are not feasible, the circuits 
should be tested at least once per day, and preferably oftener. 

c. Data obtained from all tests must be preserved for examination by the 
Inspection Department having jurisdiction. 


These rules on testing to be applied at such places as may be designated by the Inspection Depart- 
ment having jurisdiction. 


8. Motors — 

a. Must be insulated on floors or base frames, which must be kept filled 
to prevent absorption of moisture; and must be kept clean and dry. Where 
frame insulation is impracticable the Inspection Department having jurisdic- 
tion may, in writing, permit its omission, in which case the frame must be per- 


manently and effectively grounded. 


A high-potential machine which, on account of great weight or for other reasons, cannot have its 
frame insulated, should be surrounded with an insulated platform. This may be made of wood 
mounted on insulating supports, and so arranged that a man must stand upon it in order to touch any 


part of the machine. e Ane 
In case of a machine having an insulated frame, if there is trouble from static electricity due to belt 


friction, it should be overcome by placing near the belt a metallic comb connected to the earth, or by 
grounding the frame through a very high resistance of not less than 200 ohms per volt generated by the 


machine. 
b. Must be wired under the same precautions as required by rules in 
class “C”, for wires carrying a current of the same volume and potential. 


The leads or branch circuits should be designed to carry a current at least fifty per cent greater than 
that required by the rated capacity of the motor to provide for the inevitable overloading of the motor at 


times without overfusing the wires. 
c. The motor and resistance box must be protected by a cutout and con- 


trolled by a switch (see No. 17 a), said switch plainly indicating whether “on i 
or “off” Where one-fourth horse-power or less is used on low-tension circuits 


APPENDIX TT. 455 


a single-pole switch will be accepted. The switch and rheostat must be located 
within sight of the motor, except in such cases where special permission to 
locate them elsewhere is given in writing by the Inspection Department hav- 
ing jurisdiction. 

@. Must have their rheostats or starting-boxes located as to conform to the 
requirements of No. 4. 


In connection with motors the use of circuit-breakers, automatic starting-boxes and automatic 
under-load switches is recommended, and they west be used when required. 


ée. Must not be run in series-multiple or multiple-series, except on constant- 
potential systems, and then only by special permission of the Inspection De- 
partment having jurisdiction. 

J. Must be covered with a waterproof cover when not in use, and, if 
deemed necessary by the Inspection Department having jurisdiction, must be 
inclosed in an approved case. 


From the nature of the question the decision as to what is an approved case must be left to the 
Inspection Department having jurisdiction to determine in each instance. 


g. Must, when combined with ceiling fans, be hung from insulated hooks, 
or else there must be an insulator interposed between the motor and its 
support. 

hk. Must each be provided with a name-plate, giving the maker’s name, 
the capacity in volts and amperes, and the normal speed in revolutions per 
minute. 


9. Railway Power Plants — 


a. Must be equipped in each feed wire before it leaves the station with an 
approved automatic circuit-breaker (see No. 52) or other device, which will 
immediately cut off the current in case of an accidental ground. This device 
must be mounted on a fireproof base, and in full view and reach of the 
attendant. 


10. Storage or Primary Batteries — 


a. When current for light and power is taken from primary or secondary 
_ batteries, the same general regulations must be observed as applied to similar 
apparatus fed from dynamo generators developing the same difference of 
potential. 

6. Storage battery rooms must be thoroughly ventilated. 

c. Special attention is directed to the rules for rooms where acid fumes 
exist (see No. 24, 7 and &). 

d, All secondary batteries must be mounted on non-absorptive, non- 
combustible insulators, such as glass or thoroughly vitrified and glazed 
porcelain. 

é. The use of any metal liable to corrosion must be avoided in cell connec- 
tions of secondary batteries. 


11, Transformers — 
(For construction rules, see Vo. 62.) 
a. In central or substations the transformers must be so placed that smoke 
from the burning out of the coils or the boiling over of the oil (where oil-filled 
cases are used) could do no harm, 


456 ELECTRIC LIGHTING, 
(SEAS ei, 


OUTSIDE WORK. 


ALL SYSTEMS AND VOLTAGES. 
12, Wires — 

a. Service wires must have an approved rubber insulating covering (see 
No, 41). Line wires, other than services, must have an approved weatherproof, 
or rubber insulating covering (Nos. 41 and 44). All the wires must have an 
insulation equal to that of the conductors they confine. 

6. Must be so placed that moisture cannot form a cross connection be- 
tween them, not less than a foot apart, and not in contact with any substance 
other than their insulating supports. Service blocks must be covered over 
their entire surface with at least two coats of waterproof paint. 

c. Must be at least seven feet above the highest point of flat roofs, and at 
least one foot above the ridge of pitched roofs over which they pass or to 
which they are attached. 

d. Must be protected by dead insulated guard iron or wires from possibility 
of contact with other conducting wires or substances to which current may leak. 
Special precautions of this kind must be taken where sharp angles occur, or 
where any wires might possibly come in contact with electric light or power 
wires. 

é. Must be provided with petticoat insulators of glass or porcelain. Por- 
celain knobs or cleats and rubber hooks will not be approved. 

J. Must beso spliced or joined as to be both mechanically and electrically 
secure without solder. The joints must then be soldered, to insure preserva- 
tion, and covered with an insulation equal to that on the conductors. 


All joints must be soldered, even if made with some form of patent splicing device. ‘This ruling 
applies to joints and splices in all classes of wiring covered by these rules. 


g. Must, where they enter buildings, have drip loops outside, and the holes 
through which the conductors must be bushed with non-combustible, non- 
absorptive insulating tubes slanting upward toward the inside. 

hi. Telegraph, telephone, and similar wires must not be placed on the same 
cross-arm with electric light or power wires ; and when placed on the same pole 
with such wires the distance between the two inside pins of each cross-arm 
must not be less than twenty-six inches. 

z. The metallic sheaths to cables must be permanently and effectively 
connected to “earth.” 


TROLLEY WIRES: 


7. Must not be smaller than No. 0 B. & S. copper or No. 4 B. & S. silicon 
bronze, and must readily stand the strain put upon them when in use. 

k. Must have a double insulation from the ground. In wooden-pole con- 
struction the pole will be considered as one insulation. 

7. Must be capable of being disconnected at the power plant, or of being 
divided into sections, so that, in case of fire on the railway route, the current 
may be shut off from the particular section and not interfere with the work of 
the firemen. This rule also applies to feeders. 


4 —_—- 


APPENDIX I. 457 


m. Must be safely protected against accidental contact where crossed by 
other conductors. 


’ Guard wires should be insulated from the ground, and should be electrically disconnected in sections 
of not more than 300 feet in length. 


GROUND RETURN WIRES. 


mz. For the diminution of electrolytic corrosion of underground metal work, 
ground return wires must be so arranged that the difference of potential be- 
tween the grounded dynamo terminal and any point on the return circuit will 
not exceed twenty-five volts. 


It is suggested that the positive pole of the dynamo be connected to the trolley line, and that 
whenever pipes or other underground metal work are found to be electrically positive to the rails or 
surrounding earth, that they be connected by conductors arranged so as to prevent as far as possible 
current flow from the pipes into the ground. 


13. Transformers — 
(Lor construction rules, see Vo. 62.) 
a. Must not be placed inside of any building, excepting central stations, 
unless by special permission of the Inspection Department having jurisdiction. 
6. Must not be attached to the outside walls of buildings, unless separated 
therefrom by substantial supports. 


13 A. Grounding Low Potential Circuits. 

The grounding of low potential circuits under the following regulations is only allowed 
when so arranged that under normal conditions there will be no flow of current through 
the ground wire. 

Direct Current 3-Wire Systems. 

a. Neutral wire may be grounded, and when grounded the following rules 
must be complied with: — 

1. Must be grounded at the Central Station on a metal plate buried in coke 
beneath permanent moisture level, and also through all available underground 
water and gas-pipe systems. 

2. In underground systems the neutral wire must also be grounded at each 
distributing-box through the box. yp 
. 3. In overhead systems the neutral wire must be grounded every 500 feet, 

as provided in Sections ¢, ¢, and-/. 


The Inspection Department having jurisdiction may require troundine if they deem it necessary. 

Two-wire direct current systems having no accessible neutral point are not to be grounded. 
Alternating Current Secondary Systems. 

6. The neutral point of transformers, or the neutral wire of distributing 
systems, may be grounded, and when grounded the following rules must be 
complied with : — 

1. Transformers feeding 2-wire systems must be grounded at the center of 
the secondary coils. 

2 Transformers feeding systems with a neutral wire must have the neutral 
wire grounded at the transformer and at least every 250 feet beyond. 


Inspection Department having jurisdiction may regzire grounding if they deem it necessary. 


Ground Connections. 
c. The ground wire in D. C. 3-wire systems must not at Central Stations be 
smaller than the neutral wire and not smaller than No. 6 B. & S. elsewhere. 


458 ELECTRIC LIGHTING. 


ad. The ground wire in A. C. systems must never be less than No. 6 B. & S., 
and must always have equal carrying capacity to the secondary lead of the 
transformer, or the combined leads where transformers are banked. 

e. The ground wire must be kept outside of buildings, but may be di- 
rectly attached to the building or pole. The wire must be carried in as 
nearly a straight line as possible, and kinks, coils and sharp bends must be 
avoided. 

fy. The ground connection for Central Stations, transformer sub-stations, and 
banks of transformers must be made through metal plates buried in coke below 
permanent moisture level, and connection should also be made to all available 
underground piping systems. For individual transformers and building ser- 
vices the ground connection may be made as above, or may be made to water 
or other piping systems running into the buildings. This connection may be 
made by carrying the ground wire into the cellar and connecting on the street 
side of meters, main clocks, etc. 


In connecting ground wires to piping systems, where possible the wires should be soldered into 
one or more brass plugs and the plugs forcibly screwed into a pipe-fitting, or where the pipes are cast 
iron into a hole tapped to the pipe itself. For large stations, where connecting to underground pipes 
with bell and spigot joints, it is well to connect to several lengths, as the pipe joints may be of rather 
high resistance. Where such plugs cannot be used the surface of the pipe may be filed or scraped 
bright, the wire wound around it, and a strong clamp put over the wire and firmly bolted together. 

Where ground plates are useda No. 16 copper plate, about 3 x 6 feet in size, with about two feet of 
crushed coke or charcoal about pea size both under and over it, would make a ground of sufficient 
capacity for a moderate size station, and would probably answer for the ordinary sub-station or bank of 
transformers. For a large Central Station considerable more area might be necessary, depending upon 
the other underground connections available. The ground wire should be riveted to such a plate ina 
number of places, and soldered for its whole length. Perhaps even better than a copperplate is a cast- 
iron plate with projecting forks, the idea of the fork being to distribute the connection to the ground over 
a fairly broad area, and to give a large surface contact. The ground wire can probably best be connected 
to such a cast-iron plate by brass plugs screwed into the plate to which the wire is soldered. In al] 
cases the joint between the plate and the ground wire should be thoroughly protected against corrosion 
by suitable painting with waterproof paint or some equivalent. 


G@rass--C. 
INSIDE WORK 


ALL SYSTEMS AND VOLTAGES. 


GENERAL RULES — ALL SYSTEMS AND VOLTAGES. 
14. Wires — 
(For special rules See Nos. 18, 24, 32, 38, and 89.) 
a. Must not be of smaller size than No. 14 B. & S., except as allowed 
under Rules 24 ¢ and 454, 


6. Tie wires must have an insulation equal to that of the conductors they 
confine. 

c. Must be so spliced or joined as to be both mechanically and electrically 
secure without solder; they must be then soldered to insure preservation, and 
the joint covered with an insulation equal to that on the conductors. 

Stranded wires must be soldered before being fastened under clamps or 
binding screws ; and, when they have a conductivity greater than No. 10 B. & 
S. copper wire, they will be soldered into lugs. 


APPENDIX I. 459 


All joints must be soldered, even if made with some form of patent splicing device. This ruling 
applies to joints and splices in all classes of wiring covered by these rules. 


dad. Must be separated from contact with walls, floors, timbers, or partitions 

through which they may pass by non-combustible, non-absorptive insulating 
tubes, such as glass or porcelain. 

Bushings must be long enough to bush the entire length of the hole in one continuous piece, or els? 

the hole must first be bushed by a continuous waterproof tube, which may be a conductor, such as iron 


pipe; the tube then is to have a non-conducting bushing pushed in at each end so as to keep the wire 
absolutely out of contact with the conducting pipe. 


é. Must be kept free from contact with gas, water, or other metallic piping, 
or any other conductors or conducting material which they may cross, by some 
continuous and firmly fixed non-conductor, creating a separation of at least 
one inch. Deviations from this rule may sometimes be allowed by special 
permission. 

F. Must be so placed in wet places that an air space will be left between 
conductors and pipes in crossing, and the former must be run in such a way 
that they cannot come in contact with the pipe accidentally. Wires should be 
run over, rather than under, pipes upon which moisture is likely to gather or 
which, by leaking, might cause trouble on a circuit. 


15. Underground Conductors — 


a. Must be protected, when brought into a building, against moisture and 
mechanical injury, and all combustible material must be kept removed from the 
immediate vicinity. 

6. Must not be so arranged as to shunt the current through a building 
around any catch-box. 


16. Table Carrying Capacity of Wires — 


Below is a table which must be followed in placing interior conductors, 
showing the allowable carrying capacity of wires and cables of ninety-eight per 
cent conductivity, according to the standard adopted by the American Institute 
of Electrical Engineers. 


TABLE A. TABLE B. TABLE A. TABLE B. 
RUBBER- WEATHER- RUBBER- W EATHER- 
CovERED PROOF | 1 *CrRcoLar Gircuian CovERED 

WIRES. WIRES. Mits. MILs. WIRES. 
See No. 41, SEE Sze No, 41. 
No. 42 To 44. 
AMPERES. AMPERES, AMPERES. - AMPERES. 








1,624 200,000 200 300 
2,583 300,000 270 400 
4,107 400,000 330 500 
6,530 500.000 390 590 
10,380 600,000 450 680 
16,510 700,000 500 760 
26,250 800,000 550 840 
33,100 900,000 600 920 
41,740 1,000,000 650 1,000 
52,630 1,100,000 690 1,080 
66,370 1,200,000 730 1,150 
83,690 1,300,000 770 1,220 
105,500 1,400,000 810 1,290 
133,100 1,500,000 850 1,360 
167,800 1,600,000 890 1,430 
211,600 1,700,000 930 1,490 
1,800,000 970 1,550 

1,900,000 1,010 1,610 

2,000,000 1,050 1,670 








18 
16 
14 
12 
10 
8 
6 
5 
4 
3 
2 
1 
0 
00 
000 


S 
S 
SC 














460 ELECTRIC. LIGHTING. 


The lower limit is specified for rubber-covered wires to prevent gradual deterioration of the high 
insulations by the heat of the wires, but not from fear of igniting the insulation. The question of drop 
is not taken into consideration in the above tables. 

The carrying capacity of sixteen and eighteen wire is given, but no smaller than fourteen is to be 
used, except as allowed under Rules 24 ¢ and 45 6. 


17. Switches, Cutouts, Circuit-Breakers, etc. 
(For construction rules, see Vos, 51, 52, and 58.) 

a. Must, whenever called for, unless otherwise provided (for exceptions, 
see No. 8c and No. 22 c), be so arranged that the cutouts will protect, and the 
opening of the switch or circuit-breaker will disconnect, all of the wires; that 
is, in a two-wire system the two wires, and in a three-wire system the three 
wires, must be protected by the cutout, and disconnected by the operation of 
the switch or circuit-breaker. 

6. Must not be placed in the immediate vicinity of easily ignitible stuff or 
where exposed to inflammable gases or dust or to flyings of combustible 
material. 

c. Must, when exposed to dampness, either be inclosed ina waterproof 
box or mounted on porcelain knobs. 


CONSTANT CURRENT SYSTEMS. 
Principally Series Arc Lighting. 


(See also (Vos. 14, 15, and 16.) 


a. Must have an approved rubber insulating covering (see No. 41). 

6. Must be arranged to enter and leave the building through an approved 
double-contact service switch (see No. 51), mounted in a non-combustible case, 
kept free from moisture, and easy of access to police or firemen. So-called 
‘snap switches’ must not be used on high-potential circuits. 

c. Must always be in plain sight, and never incased, except when required 
by the Inspection Department having jurisdiction. 

@d. Must be supported on glass or porcelain insulators, which separate the 
wire at least one inch from the surface wired over, and must be kept vzezdly at 
least eight inches from each other, except within the structure of lamps, 
on hanger-boards, in cutout boxes, or like places, where a less distance is 
necessary, 

é. Must, on side walls, be protected from mechanical injury by a sub- 
stantial boxing, retaining an air space of one inch arounc the conductors, 
closed at the top (the wires passing through bushed holes), and extending not 
less than seven feet from the floor. When crossing floor-timbers in cellars or 
in rooms, where they might be exposed to injury, wires must be attached by 
their insulating supports to the under side of a wooden strip not less than one- 
half an inch in thickness. 


18. Wires — 


19. Arc Lamps — 
(For construction rules, see No. 57.) 
a. Must be carefully isolated from inflammable material. 
6. Must be provided at all times with a glass globe surrounding the arc, 


securely fastened upon a closed base. No broken or cracked globes to be 
used. 
c. Must be provided with a wire netting (having a mesh not exceeding one 


and one-fourth inches) around the globe, and an approved spark arrester (see 
No. 58), when readily inflammable material is in the vicinity of the lamps, to 


APPENDIX I. 461 


prevent escape of sparks, melted copper, or carbon. It is recommended that 
plain carbons, not copper-plated, be used for lamps in such places. 
Arc lamps, when used in places where they are exposed to flyings of easily inflammable material, 


should have the carbons inclosed completely in a giobe in such manner as to avoid the necessity for 
spark arresters. 


For the present, globes and spark arresters will not be required on so-called ‘‘ inverted arc” 
lamps, but this type of lamp must not be used where exposed to flyings of easily inflammable materials. 

d. Where hanger-boards (see No. 56) are not used, lamps must be hung 
from insulating supports other than their conductors. 


20. Incandescent Lamps in Series Circuits — 


a. Must have the conductors installed as provided in No. 18, and each 
lamp must be provided with an automatic cutout. 


6, Must have each lamp suspended from a hanger-board by means of rigid 
tube. 
c. No electro-magnetic device for switches and no system of multiple- 


series or series-multiple lighting will be approved. 
@. Under no circumstances can they be attached to gas fixtures. 


CONSTANT POTENTIAL SYSTEMS. 
GENERAL RULES FALL. VOLTAGES, 
21. Automatic Cutouts (Fuses and Circuit-Breakers). 
(See Vo. 17, and for construction Nos. 52 and 538.) 


a. Must be placed on all service wires, either overhead or underground, 
as near as possible to the point where they enter the building and inside the 
walls, and arranged to cut off the entire current from the building. 

Where the switch required by rule No. 22 is inside the building, the cutout required by this section 
must be placed so as to protect it. 

6. Must be placed at every point where a change is made in the size of 
wire [unless the cutout in the larger wire will protect the smaller (see No. 16)]. 

c. Must be in plain sight, or inclosed in an approved box (see No. 54) and 
readily accessible. They must not be placed in the canopies or shells of 
fixtures. 

d. Must be so placed that no set of incandescent lamps, whether grouped 
on one fixture or several fixtures or pendants, requiring more than 660 watts, 
shall be dependent upon one cutout. Special permission may be given in 
writing by the Inspection Department having jurisdiction for departure from 
this rule in case of large chandeliers, stage borders, and illuminated signs. 

é. Must be provided with fuses, the rated capacity of which does not ex- 
ceed the allowable carrying capacity of the wire; and, when circuit-breakers 
are used, they must not be set more than about thirty per cent above the allow- 
able carrying capacity of the wire, unless a fusible cutout is also installed in 
the circuit (see No. 16). 


22. Switches — . 
(See Wo. 17, and for construction, No. &1.) 

a. Must be placed on all service wires, either overhead or underground 
in a readily accessible place, as near as possible to the point where the wires 
enter the building, and arranged to cut off the entire current. 

6. Must always be placed in dry, accessible places, and be grouped as far 
as possible. Knife switches must be so placed that gravity will tend to open 
rather than close the switch. 


462 ELECTRICLLIOGH LNG 


c. Must not be single-pole, except when the circuits which they control 
supply not more than six 16-candle power lamps or their equivalent. 

ad. Where flush switches are used, whether with conduit systems or not, 
the switches must be inclosed in boxes constructed of or lined with fire-resisting 
material. No push-buttons for bells, gas-lighting circuits or the like shall 
be placed in the same wall-plate with switches controlling electric light or | 
power wiring. 


23. Electric Heaters — 


a. Must, if stationary, be placed in a safe situation, isolated from inflam- 
mable materials, and be treated as sources of heat. 

6. Must each have a cutout and zzadzcating-switch (see No. 17a). 

c. Must have the attachments of feed wires to the heaters in plain sight, 
easily accessible, and protected from interference, accidental or otherwise. 

ad. The flexible conductors for portable apparatus, such as irons, etc., must 
have an approved insulating covering (see No. 45). 

ée. Must each be provided with name-plate, giving the maker’s name and 
the normal capacity in volts and amperes. 


LOW-POTENTIAL SYSTEMS. 
550 Volts or less. 


Any circuit attached to any machine, or combination of machines, which 
develops a difference of potential, between any two wztres, of over ten 
volts and less than 550 volts, shall be considered as a low-potential 
circuit, and as coming under thts class, unless an approved transform- 
ing device is used, which cuts the difference of potential down to ten 
volts or less. The primary circuit not to exceed a potential of 3,500 
volts. 


24, Wires — 
GENERAL RULES. 


(See also Nos. 14, 15, and 16.) 


a. Must not be laid in plaster, cement, or similar finish. 

6. Must never be fastened with staples. 

c. Must not be fished for any great distance, and only in places where the 
inspector can satisfy himself that the rules have been complied with. 

@d. Twin wires must never be used, except in conduits, or where flexible 
conductors are necessary. 

é. Must be protected on side walls from mechanical injury. When cross- 
ing floor-timbers in cellars or in rooms, where they might be exposed to injury, 
wires must be attached by their insulating supports to the under side of a 
wooden strip, not less than one-half inch in thickness, and not less than three 
inches in width. 


Suitable pretection on side walls may be secured by a substantial boxing, retaining an air space of 
one inch around the conductor, closed at the top (the wires passing through bushed holes), and extend- 
ing not less than five feet from the floor; or by an iron-armored or metal-sheathed insulating conduit 
sufficiently strong to withstand the strain it will be subjected to; or plain metal pipe, lined with insu- 
lating tubing, which must extend one-half inch beyond the end of the metal tube. 

The pipe must extend not less than five feet above the floor, and may extend through the floor in 
place of a floor bushing. 

If iron pipes are used with alternating currents, the two or more wires of a circuit ust be placed 


APPENDIX I. 465 


in the same conduit. In this case the insulation of each wire must be reinforced by a tough conduit 
tubing projecting beyond the ends of the iron pipe at least two inches. 

Ff. When run immediately under roofs, or in proximity to water tanks or 
pipes, will be considered as exposed to moisture. 


SEE CIn be RULES: 

For open work: 

Ln ary places: 

g. Must have an approved rubber or “slow-burning " waterproof insula- 
tion (see Nos, 41 and 42). 

hi. Must be rigidly supported on non-combustible, non-absorptive insula- 
tors, which separate the wires from each other and from the surface wired 
over in accordance with following table : 


OLTAGE. DISTANCE FROM SURFACE, DISTANCE BETWEEN WIRES, 
@ to 225 4 inch. 2% inches. 
225, ** 550 Ly 4 “ 


Rigid supporting requires under ordinary conditions, where wiring along flat surfaces, supports at 
least every four and one-half feet. If the wires are liable to be disturbed, the distance between supports 
should be shortened. In buildings of mill construction, mains of No. 8 B. & S, wire or over, where not 
liable to be disturbed, may be separated about four inches, and run from timber to timber, not breaking 
around, and may be supported at each timber only. 

This rule will not be interpreted to forbid the placing of the neutral of a three-wire system in the 
center of a three-wire cleat, provided the outside wires are separated in accordance with above table. 


Ln damp places, such as Breweries, Sugar Houses, Packing Houses, 
Stables, Dye Houses, Paper or Pulp Mills, or buildings specially 
liable to moisture or acta or other fumes liable toinjure the wires or 
their insulation, except where used for pendants : 


z. Must have an approved rubber insulating covering (see No. 41). 

j. Must be rigidly supported on non-combustible, non-absorptive insula- 
tors, which separate the wire at least one inch from the surface wired over, and 
they must be kept apart at least two and one-half inches. 

Rigid supporting requires under ordinary conditions, where wiring over flat surfaces, supports at 
least every four and one-half feet. If the wires are liable to be disturbed, the distance between sup- 
ports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. wire or over, 


where not liable to be disturbed, may be separated about four inches, and run from timber to timber, 
not breaking around, and may be supported at each timber only, 


k. Must have no joints or splices. 
For molding work : 


7. Must have approved rubber insulating covering (see No, 41). 

mz. Must never be placed in molding in concealed or damp places. 
For conduit work: 

z. Must have an approved rubber insulating covering (see No. 47). 

o. Must not be drawn in until all mechanical work on the building has 
been, as far as possible, completed. 

p. Must, for alternating systems, have the two or more wires of a circuit 
drawn in the same conduit. 

It is advised that this be done for direct-current systems also, so that they may be changed to 


alternating systems at any time, induction troubles preventing such a change unless this construction is 
followed. 


For concealed ‘‘ knob and tube’’ work: 
g. Must have an approved rubber insulating covering (see No. 41). 


464 ELECTRIC LIGHTING 


yr. Must be rigidly supported on non-combustible, non-absorptive insula- 
tors which separate the wire at least one inch from the surface wired over, and 
must be kept at least ten inches apart, and, when possible, should be run singly 
on separate timbers or studding. 


Rigid supporting requires under ordinary conditions, where wiring along flat surfaces, supports at 
least every four and one-half feet. If the wires are liable to be disturbed, the distance between supports 
should be shortened. 


s. When, from the nature of the case, it is impossible to place concealed 
wiring on non-combustible, insulating supports of glass or porcelain, an a@f- 
proved armored cable with single or twin conductors (see No. 48) may be used 
where the difference of potential between wires is not over 300 volts, provided it 
is installed without joints between outlets, and the cable armor properly enters 
all fittings and is rigidly secured in place; or, if the difference of potential be- 
tween wires is not over 300 volts, and if wires are not exposed to moisture, they 
may be fished on the loop system if separately incased throughout in approved 
flexible tubing or conduits. 

For fixture work: 

¢t. Must have an approved rubber insulating covering (see No. 46), and 
shall not be less in size than No. 18 B. & S. 

u. Supply conductors, and especially the splices to fixture wires, must be 
kept clear of the grounded part of gas-pipes; and. where shells are used, the 
latter must be constructed in a manner affording sufficient area to allow this 
requirement. 

v. Must, when fixtures are wired outside, be so secured as not to be cut or 
abraded by the pressure of the fastenings or motion of the fixture. 


25, Interior Conduits — 
(See also Nos. 24 n to p, and 49.) 


The object of a tube or conduit is to facilitate the insertion or extraction of the conductors to pro- 
tect them from mechanical injury and, as far as possible, from moisture. Tubes or conduits are to be 
considered merely as raceways, and are not to be relied upon for insulation between wire and wire, or 
between the wire and the ground. 

a. No conduit tube having an internal diameter of less than five-eighths 
of an inch shall be used. (If conduit is lined, measurement to be taken inside 
of lining.) 

4. Must be continuous from one junction box to another or to fixtures, 
and the conduit tube must properly enter all fittings. 


c. Must be first installed as a complete conduit system, without the con- 
ductors. 


dad. Must be equipped at every outlet with an approved outlet box. 

é. Metal conduits, where they enter junction boxes, and at all other out- 
lets, etc., must be fitted with a capping of approved insulating material, fitted 
so as to protect wire from abrasion. 

f. Must have the metal of the conduit permanently and effectively 
grounded. 

26, Fixtures — 
(See also Vo. 24 zt to v.) 

a. Must, when supported from the gas-piping of a building, be insulated 
from the gas-pipe system by means of approved insulating joints (see No. 59) 
placed as close as possible to the ceiling. 


It is recommended that the gas outlet pipe be protected above the insulating joint by a non-com- 
bustible, non-absorptive insulating tube, having a flange at the lower end where it comes in contact with 


APPENDIX I. 465 


the insulating joint ; and that, where outlet tubes are used, they be of sufficient length to extend below 
the insulating joint, and that they be so secured that they will not be pushed back when the canopy is 
put in place. Where iron ceilings are used, care must be taken to see that the canopy is thoroughly and 
permanently insulated from the ceiling. 


6. Must have all burs, or fins, removed before the conductors are drawn 
into the fixture. 

c. The tendency to condensation within the pipes should be guarded 
against by sealing the upper end of the fixture. 

ad. No combination fixture in which the conductors are concealed in a space 
less than one-fourth inch between the inside pipe and the outside casing will 
be approved. 

é. Must be tested for “contacts” between conductors and fixture, for 
‘short circuits,” and for ground connections before it is connected to its 
supply conductors. 

f. Ceiling blocks for fixtures should be made of insulating material; if not 
the wires in passing through the plate must be surrounded with non-combustible 
non-absorptive, insulating material, such as glass or porcelain. 

g. Under no conditions shall there be a difference of potential of more 
than 300 volts between wires contained in or attached to the same fixture 


27. Sockets — 
(For construction rules, see No. 55.) 

a. In rooms where inflammable gases may exist the incandescent lamp 
and socket must be inclosed in a vapor-tight globe, and supported on a pipe 
hanger, wired with approved rubber-covered wire (see No. 41) soldered directly 
to the circuit. 

6. In damp or wet places, or over specially inflammable stuff, waterproof 
sockets must be used. 


When waterproof sockets are used, they should be hung by separate stranded rubber-covered 
wires, not smaller than No. 14 B. & S., which should preferably be twisted together when the drop is 
over three feet. These wires should be soldered direct to the circuit wires, but supported independently 
of them. 


28. Flexible Cord — 


a. Must have an approved insulation and covering (see No. 45). 

6. Must not be used where the difference of potential between the two 
wires is over 300 volts. 

c. Must not be used as a support for clusters. 

ad. Must not be used except for pendants, wiring of fixtures, and portable 
lamps or motors. 

e. Must not be used in show windows. 

jf. Must be protected by insulating bushings where the cord enters the 
socket. 

g. Must be so suspended that the entire weight of the socket and lamp will 
be borne by knots under the bushing in the socket, and above the point where 
the cord comes through the ceiling block or rosette, in order that the strain 
may be taken from the joints and binding screws. 


29. Arc Lights on Low-Potential Circuits — 


a. Must have a cutout (see No. 17a) for each lamp or each series of 
amps. 


466 ELECTRIC LIGHTING 


The branch conductors should have a carrying capacity about fifty per cent in excess of the normal 
current required by the lamp to provide for heavy current required when lamp is started or when carbons 
become stuck without overfusing the wires. 


6. Must only be furnished with such resistances or regulators as are in- 
closed in non-combustible material, such resistances being treated as sources 
of heat. Incandescent lamps must not be used for resistance devices. 

c. Must be supplied with globes and protected by spark arresters and wire 
netting around globe, as in the case of arc lights on high-potential circuits (see 
Nos. 19 and 58). 


30. Economy Coils — 


a. Economy and compensator coils for arc lamps must be mounted on 
non-combustible, non-absorptive insulating supports, such as glass or porcelain, 
allowing an air space of at least one inch between frame and support, and in 
general to be treated like sources of heat. 


31. Decorative Series Lamps — 


a. Incandescent lamps run in series shall not be used for decorative pur- 
poses inside of buildings, except by special permission in writing from the 
Inspection Department having jurisdiction. 


32, Car Wiring — 
a. Must be always run out of reach of the passengers, and must have an 
approved rubber-insulating covering (see No. 41) 


33. Car Houses — 


a. Must have the trolley wires securely supported on insulating hangers. 

6. Must have the trolley hangers placed at such distance apart that, in 
case of a break in the trolley wire, contact cannot be made with the floor. 

c. Must have cutout switch located at a proper place outside of the build- 
ing, so that all trolley circuits in the building can be cut out at one point, and 
line circuit-breakers must be installed, so that when this cutout switch is open 
the trolley wire will be dead at all points within 100 feet of the building. The 
current must be cut out of the building whenever the same is not in use or the 
road not in operation. 

ad. Must have all lamps and stationary motors installed in such a way that 
one main switch can control the whole of each installation —lighting or 
power —independently of main feeder-switch. No portable incandescent 
lamps or twin wire allowed, except that portable incandescent lamps may be 
used in the pits, connections to be made by two approved rubber-covered flex- 
ible wires (see No. 41), properly protected against mechanical injury; the cir- 
cuit to be controlled by a switch placed outside of the pit. 

e. Must have all wiring and apparatus installed in accordance with rules 
under Class “C” for constant potential systems. 

f. Must not have any system of feeder distribution centering in the 
building. 

g. Must have the rails bonded at each joint with no less than No.2 B. &S. 
annealed copper wire, also a supplementary wire to be run for each track. 

h. Must not have cars left with trolley in electrical connection with the 
trolley wire. 


APPENDIX I. 467 


34, Lighting and Power from Railway Wires — 


a. Must not be permitted, under any pretense, in the same circuit with 
trolley wires with a ground return, except in electric railway cars, electric car 
houses and their power stations; nor shall the same dynamo be used for both 
purposes. 


HIGH-POTENTIAL SYSTEMS. 
550 TO 3,500 VoLTs. 

Any circuit attached to any machine, or combination of machines, which de- 
velops a aifference of potential, between any two wrres, of over 300 volts 
and less than 3,500 volts, shall be considered as a high-potential circuit, 
and as coming under that class, unless an approved transforming device 
7s used, which cuts the difference of potential down to 300 volts or less. 

35. Wires — 

(See also Nos. 14, 15, and 16.) 

a. Must have an approved rubber-insulating covering (see No. 41). 

6. Must be always in plain sight and never incased, except where required 
by the Inspection Department having jurisdiction. 

c. Must be rigidly supported on glass or porcelain insulators, which raise 
the wire at least one inch from the surface wired over, and must be kept apart 
at least four inches for voltages up to 750 and at least eight inches for voltages 
over 750, 

Rigid supporting requires under ordinary conditions, where wiring along flat surfaces, supports 


at least about every four and one-half feet. If the wires are unusually liable to be disturbed, the dis- 
tance between supports should be shortened. 


In buildings of mill construction, mains of No. 8 B. & S. wire or over, where not liable to be dis- 
turbed, may be separated about six inches for voltages up to 750 and about ten inches for voltages above 
750 ; and run from timber to timber, not breaking around, and may be supported at each timber only. 

@. Must be protected on side walls from mechanical injury by a substantial 
boxing, retaining an air space of one inch around the conductors, closed at the 
top (the wires passing through bushed holes) and extending not less than seven 
feet from the floor. When crossing floor-timbers, in cellars or in rooms, where 
they might be exposed to injury, wires must be attached by their insulating 

supports to the under side of a wooden strip not less than one-half an inch in 
- thickness. 


36, Transformers (when permitted inside buildings, see No. 13) — 
(For construction rules, see No. 62.) 

a. Must be located ata point as near as possible to that at which the pri- 
mary wires enter the building. 

6. Must be placed in an inclosure constructed of or lined with fire-resisting 
material: the inclosure to be used only for this purpose, and to be kept securely 
locked, and access to the same allowed only to responsible persons. 

c. Must be effectually insulated from the ground, and the inclosure in 
which they are placed must be practically air-tight, except that it shall be 
thoroughly ventilated to the outdoor air, if possible, through a chimney or flue. 
There should be at least six inches air space on all sides of the transformer. 
o7. Series Lamps — 

a. No system of multiple-series or series-multiple for light or power will 
be approved. 

6. Under no circumstances can lamps be attached to gas fixtures. 


468 ELECT RICQLAGHIING. 


EXTRA HIGH-POTENTIAL SYSTEMS. 
OVER 3,500 VOLTS. 


Any circuit attached to any machine or combination of machines, which de. 
velops a difference of potential, between any two wires, of over 3,500 
volts, shall be considered as an extra high-potential circuit, and as 
coming under that class, unless an approved transforming device ts 
used, which cuts the difference of potential down to 3,500 volts or less. 


38, Primary Wires — 


a. Must not be brought into or over building, except power and substations. 


39. Secondary Wires — 


a. Must be installed under rules for high-potential systems, when their 
immediate primary wires carry a current of over 3,500 volts, unless the primary 
wires are entirely underground, within city and village limits. 


The presence of wires carrying a current with a potential of over 3,500 volts in the streets of cities, 
towns, and villages is considered to increase the fire hazard. Extra high potential circuits are also 
objectionable in any location where telephone, telegraph, and similar circuits run in proximity to them. 
As the underwriters have no jurisdiction over streets and roads they can only take this indirect way of 
discouraging such systems ; but further, it is strongly urged that municipal authorities absolutely refuse 
to grant any franchise for right of way for overhead wires carrying a current of extra high potential 


through streets or roads which are used to any great extent for public travel or for trunk-line, telephone, 
or telegraph circuits. 


Crass D. 


FITTINGS, MATERIALS, AND DETAILS OF 
CONSTRUCTION. 


All Systems and Voltages. 


Insulated Wires— Rules 4o to 48. 
40. General Rules — . 


a. Copper for insulated conductors must never vary in diameter so as to 
be more than two one-thousandths of an inch less than the specified size. 

6. Wires and cables of all kinds designed to meet the following specifica- 
tions must be plainly tagged or marked as follows: 


1, The maximum voltage at which the wire is designed to be used. 
2. The words “ National Electrical Code Standard.” 


3. Name of the manufacturing company, and, if desired, trade-name of 
the wire. 


4, Month and year when manufactured. 


41. Rubber-Covered — 


a. Copper for conductors must be thoroughly tinned. 


APPENDIX 1. 469 


Insulation for voltages between o and 600: 


6. Must be of rubber or other approved substance, and be of a thickness 
not less than that given in the following table for B. & S. gauge sizes: 


From 18 to 16, inclusive, 3%” 
th 14 to 8, “ da” 
a Weta 2. S re” 
“ 1 to 0000, « fe’ 
es 0000 to 500,000, C. M. oa” 
“ 500,000 to 1,000,000,  “ da’ 
Larger than 1,000,000, y’ 


Measurements of insulating wall are to be made at the thinnest portion of 
the dielectric. . 

c. The completed coverings must show an insulation resistance of at least 
100 megohms per mile during thirty days’ immersion in water at seventy 
degrees Fahrenheit. 

@. Each foot of the completed covering must show a dielectric strength 
sufficient to resist throughout five minutes the application of an electro-motive 
force of 3,000 volts per one-sixty-fourth of an inch thickness of insulation under 
the following conditions : 


The source of alternating electro-motive force shall be a transformer of at 
least one kilowatt capacity. The application of the electro-motive force shall 
first be made at 4,000 volts for five minutes and then the voltage increased by 
steps of not over 3,000 volts, each held for five minutes, until the rupture of the 
insulation occurs. The tests for dielectric strength shall be made on a sample 
of wire which has been immersed for seventy-two hours in water, one foot of 
which is submerged in a conducting liquid held in a metal trough, one of the 
transformer terminals being connected to the copper of the wire and the other 
to the metal of the trough. 


Insulations for voltages between 600 and 3,500: 


e. The thickness of the insulating walls must not be less than those given 

in the following table for B. & S. gauge sizes: 

From 14 to 1, inclusive, 2” 

From 0 to 500,000, C. M., ss” covered by a tape or a braid. 
Larger than 500,000, C. M., s:” covered by a tape or a braid. 

f. The requirements as to insulation and break-down resistance for wires 
for low-potential systems shall apply, with the exception that an insulation re- 
sistance of not less than 300 megohms per mile shall be required. 

g. Wire for arc-light circuits exceeding 3,500 volts potential shall have an 
insulating wall not less than six-thirty-seconds of an inch in thickness, and 
shall withstand a break-down test of at least 30,000 volts and have an insula- 
tion of at least 500 megohms per mile. 

The tests on this wire to be made under the same conditions as for low- 
potential wires. 


Specifications for insulations for alternating currents exceeding 3,500 volts have been considered, 
but on account of the somewhat complex conditions in such work, it has so far been deemed inexpedient 
to specify general insulations for this use. 


470 ELECTRICWIGHILNVG, 


h. All of the above insulations must be protected by a substantial braided 
covering properly saturated with a preservative compound and sufficiently 
strong to withstand all the abrasion likely to be met with in practice, and 
sufficiently elastic to permit all wires smaller than No.7 B. & S. gage to be 
bent around a cylinder with twice the diameter of the wire, without injury to 
the braid. 


42, Slow-burning Weatherproof — 


a. The insulation shall consist of two coatings, the inner one to be fire- 
proof in character, the outer to be weatherproof. The inner fireproof coating 
must comprise at least six-tenths of the total thickness of the wall. The com- 
pleted covering must be of a thickness not less than that given in the following 
table for B. & S. gauge sizes: 


From 14 to 8, inclusive, &” 
+ 7 to Ze Tea 
cs 2 to 0000, ex” 
es 0000'to 500,000, C.M., =” 
4 500,000 to 1,000,000,  “ oa” 

Larger than 1,000,000,“ 4’ 


Measurements of insulating wall are to be made at the thinnest portion of 
the dielectric. 

6. The inner fireproof coating shall be layers of cotton or other thread, the 
outer one of which must be braided. All the interstices of these layers are to 
be filled with the fireproofing compound. This is to be material whose solid 
constituent is not susceptible to moisture, and which will not burn even when 
ground in an oxidizable oil, making a compound which, while proof against 
fire and moisture, at the same time has considerable elasticity, and which when 
dry will suffer no change at a temperature of 250 degrees Fahrenheit, and 
which will not burn at even higher temperature. 

c. The weatherproof coating shall be a stout braid thoroughly saturated 
with a dense moistureproof compound thoroughly slicked down, applied in 
such manner as to drive any atmospheric moisture from the cotton braiding, 
thereby securing a covering to a great degree waterproof and of high insulat- 
ing power. This compound to retain its elasticity at zero Fahrenheit, and 
not to drip at 160 degrees Fahrenheit. 


This wire is not as burnable as the old ‘‘ weatherproof,’’ nor as subject to softening under heat, 
but still is able to repel the ordinary amount of moisture found indoors. It would not usually be used 
for outside work. 


43. Slow-burning — 

a. The insulation shall be the same as the ‘‘slow-burning weatherproof,” 
except that the outer braiding shall be impregnated with a fireproofing com- 
pound similar to that required for the interior layers, and with the outer sur- 
face finished smooth and hard. 


This ‘‘ slow-burning ’’ wire shall only be used with special permission of the Inspection Depart- 
ment having jurisdiction. 

This is practically the old ‘‘ Underwriters’ ’’ insulation. It is specially useful in hot, dry places 
where ordinary insulations would perish, also where wires are bunched, as on the back of a large 


APPENDIX I. Ae 


switchboard or in a wire tower, so that the accumulation of rubber or weatherproof insulation would 
result in an objectionably large mass of highly inflammable material. 
Its use is restricted, as its insulating qualities are not high and are damaged by moisture. 


44. Weatherproof — 


a. The insulating covering shall consist of at least three braids thoroughly 
impregnated with a dense moisture repellent, which will not drip at a temper- 
ature lower than 180 degrees Fahrenheit. The thickness of insulation shall be 
not less than that of “slow-burning weatherproof.” The outer surface shall 
be thoroughly slicked down.” 


This wire is for outdoor use where moisture is certain and where fireproof qualities are not neces- 
sary. 


45, Flexible Cord — 


a. Must be made of stranded copper conductors, each strand to be not 
larger than No. 26 or smaller than No. 30 B. & S. gauge, and-each stranded 
conductor must be covered by an approved insulation and protected from 
mechanical injury by a tough braided outer covering. 


For pendent lamps: 

In this class is to be included all flexible cord which under usual condi- 
tions hangs freely in air, and which is not likely to be moved sufficiently to 
come in contact with surrounding objects. 

6. Each stranded conductor must have a carrying capacity equivalent to 
not less than a No. 18 B. & S. gauge wire. 

c. The covering of each stranded conductor must be made up as follows : 


1, A tight, close wind of fine cotton. 

2. The insulation proper, which shall be either waterproof or slow- 
burning. 

8. An outer cover of silk or cotton. 


The wind of cotton tends to prevent a broken strand puncturing the insulation and causing a 
short circuit. It also keeps the rubber from corroding the copper. 


d. Waterproof insulation must be solid, at least one-thirty-second of an 
inch thick, and must show an insulation resistance of fifty megohms per mile 
throughout two weeks’ immersion in water at 70 degrees Fahrenheit, and stand 
the tests prescribed for low-tension wires as far as they apply. 

é. Slow-burning insulation must be at least one-thirty-second of an inch in 
thickness, and composed of substantial, elastic, slow-burning materials, which 
will suffer no damage at a temperature of 250 degrees Fahrenheit. 

yf. The outer protecting braiding should be so put on and sealed in place 
that when cut it will not fray out, and where cotton is used, it should be im- 
pregnated with a flameproof paint, which will not have an injurious effect on 
the insulation. 


For portables : 

In this class is included all cord used on portable lamps, small portable 
motors, etc. 

g. Flexible cord for portable use must have waterproof insulation as 
required in section @ for pendent cord, and in addition be provided with a rein- 
forcing cover especially designed to withstand the abrasion it will be subject 
to in the uses to which it is to be put. 


AX? ELECTRICOLIGRIUING 


For portable heating apparatus: 


hk. Must be made up as follows: — 


1, A tight, close wind of fine cotton. 

A thin layer of rubber about one-one-hundredth of an inch thick, or 
other cementing material. 

A layer of asbestos insulation at least three-sixty-fourths of an inch 
thick. 

4. A stout braid of cotton. 

5, An outer reinforcing cover especially designed to withstand abrasion. 


eo 


This cord is in no sense waterproof, the thin layer of rubber being specified in order that it may 
serve merely as a Seal to help hold in place the fine cotton and asbestos, and it should beso put on as to 
accomplish this. 


46. Fixture Wire — 


a. Must have a solid insulation, with a slow-burning, tough, outer cover- 
ing, the whole to be at one-thirty-second of an inch in thickness, and show an 
insulation resistance between conductors, and between either conductor and 
the ground, of at least one megohm per mile, after one week’s submersion in 
water at seventy degrees Fahrenheit, and after three minutes’ electrification, 
with 550 volts. 


47. Conduit Wire — 


Must comply with the following specifications: 

a. For metal conduits, having a lining of insulating material, single wires 
must comply with No. 41, and all duplex, twin, and concentric conductors must 
comply with No. 41, and must also have each conductor separately braided or 
taped and a substantial braid covering the whole. 

6. For unlined metal conduits, conductors must conform to the specifica- 
tions given for lined conduits, and in addition have a second outer fibrous 
covering at least one-thirty-second of an inch in thickness, and sufficiently 
tenacious to withstand the abrasion of being hauled through the metal 
conduit. 


The braid required around each conductor in duplex, twin, and concentric cables is to hold the 
rubber insulation in place and prevent jamming and flattening. 


48. Armored Cable — 


a. The armor of such cables must be at least equal in thickness and of 
equal strength to resist penetration by nails, etc., as the armor of metal cover- 
ings of metal conduits (see No. 49 0). 

6. The conductors in same, single wire or twin conductors, must have an 
insulating covering as required by No. 41, any filler used to secure a round 
exterior must be impregnated with a moisture repellent, and’ the whole bunch 
of conductors and fillers must have a separate exterior covering of insulating 
material at least one-thirty-second of an inch in thickness, conforming to the 
insulation standard given in No. 41, and covered with a substantial braid. 


Very reliable insulation is specified, as such cables are liable to hard usage, and in part of their 
length may be subject to moisture, while they may not be easily removable, so that a breakdown of 


insulation is likely to be expensive. 


APPENDIX I. Ate 


49. Interior Conduits — 
(For wiring rules, see Nos. 24 and 28.) 
a. Each length of conduit, whether insulated or uninsulated, must have 


the maker’s name or initials stamped in the metal or attached thereto in a 
satisfactory manner, so that the inspectors can readily see the same. 


METAL CONDUITS WITH LINING OF INSULATING MATERIAL. 


6. The metal covering or pipe must be equal in strength to the ordinary 
commercial forms of gas-pipe of the same size, and its thickness must be not 
less than that of standard gas-pipe, as shown by the following table: 


Size. Thickness of Size. Thickness of 
Inches. Wall— Inches. Inches. Wall— inches. 
3 109 14 .140 
§ 111 13 145 
3 ts 2 154 
1 134 


An allowance of two-one-hundredths of an inch for variation in manufac- 
turing and loss of thickness by cleaning will be permitted. 

c. Must not be seriously affected externally by burning out a wire inside 
the tube when the iron pipe is connected to one side of the circuit. 

dad. Must have the insulating lining firmly secured to the pipe. 

e. The insulating lining must not crack or break when a length of the 
conduit is uniformly bent at temperature of 212 degrees Fahrenheit to an angle 
of ninety degrees, with a curve having a radius of fifteen inches, for pipes of 
one inch and less, and fifteen times the diameter of pipe for larger pipes. 

f. The insulating lining must not soften injuriously at a temperature 
below 212 degrees Fahrenheit, and must leave water in which it is boiled 
practically neutral. 

g. The insulating lining must be at least one-thirty-second of an inch in 
thickness, and the materials of which it is composed must be of such a nature 
as will not have a deteriorating effect on the insulation of the conductor, and 
be sufficiently tough and tenacious to withstand the abrasion test of drawing 
long lengths of conductors in and out of same. 

h. The insulating lining must not be mechanically weak after three days’ 
submersion in water, and when removed from the pipe entire must not absorb 
more than ten per cent of its weight of water during 100 hours of submersion. 

z. All elbows or bends must be so made that the conduit or lining of same 
will not be injured. The radius of the curve of the inner edge of any elbow 
not to be less than three and one-half inches. Must have not more than the 
equivalent of four quarter bends from outlet to outlet, the bends at the outlets 
not being counted. 


UNLINED METAL CONDUITS. 

j. Plain iron or steel pipes of equal thickness and strengths specified for 
lined conduits in No. 49 6 may be used as conduits, provided their interior sur- 
faces are smooth and free from burs; pipe to be galvanized, or the interior 
surfaces coated or enameled, to prevent oxidation, with some substance which 
will not soften so as to become sticky and prevent wire from being withdrawn 
from the pipe. 


AT4 ELECTRICOLRIGHZING. 


k, All elbows or bends must be so made that the conduit will not be 
injured. The radius of the curve of the inner edge of any elbow not to be less 
than three and one-half inches. Must have not more than the equivalent of 
four quarter bends from outlet to outlet, the bends at the outlet not being 
counted. 


50. Wooden Moldings — 
(Lor wiring rules, see Vo. 24.) 


a. Must have, both outside and inside, at least two coats of waterproof 
paint, or be impregnated with a moisture repellent. 

6. Must be made of two pieces, a backing and capping so constructed as 
to thoroughly incase the wire, and provide a one-half-inch tongue between the 
conductors, and a solid backing, which, under grooves, shall not be less than 
three-eighths of an inch in thickness, and must afford suitable protection from 
abrasion. 


It is recommended that only hardwood molding be used, 


51. Switches— 
(See Vos. 17 and 22.) 


a. Must be mounted on non-combustible, non-absorptive, insulating bases, 
such as slate or porcelain. 

6. Must have carrying capacity sufficient to prevent undue heating. 

c. Must, when used for service switches, indicate, on inspection, whether 
the*current.be on or oft.” 

ad. Must be plainly marked, where it will always be visible, with the name 
of the maker and the current and voltage for which the switch is designed. 

e. Must, for constant potential systems, operate successfully at fifty per 
cent overload in amperes, with twenty-five per cent excess voltage under the 
most severe conditions they are liable to meet with in practice. 

J. Must, for constant potential systems, have a firm and secure contact; 
must make and break readily, and not stop when motion has once been 
imparted by the handle. 

g. Must, for constant current systems, close the main circuit and discon- 
nect the branch wires when turned ‘ off”; must be so constructed that they 
shall be automatic in action, not stopping between points when started, and 
must prevent an arc between the points under all circumstances. They must 
indicate, upon inspection, whether the current be ‘‘on” or “ off.” 


52. Cutouts and Circuit-Breakers — 
(For installation rules, see Nos, 17 ang 21.) 


a. Must be supported on bases of non-combustible, non-absorptive insu- 
lating material. 

6. Cutouts must be provided with covers, when not arranged in approved 
cabinets, so as to obviate any danger of the melted fuse metal coming in con- 
tact with any substance which might be ignited thereby. 

c. Cutouts must operate successfully, under the most severe conditions 
they are liable to meet with in practice, on short circuits with fuses rated at 
fifty per cent above, and with a voltage twenty-five per cent above the current 
and voltage for which they are designed. 


APPENDIX I. 05 


ad. Circuit-breakers must operate successfully, under the most severe con- 
ditions they are liable to meet with in practice, on short circuits when set at 
fifty per cent above the current, and with a voltage twenty-five per cent above 
that for which they are designed. 

é. Must be plainly marked, where it will always be visible, with the name 
of the maker, and current and voltage for which the device is designed. 


53. Fuses — : - 
(for installation rules, see Nos. 17 and 21.) 


a. Must have contact surfaces or tips of harder metal having perfect 
electrical connection with the fusible part of the strip. 

6. Must be stamped with about eighty per cent of the maximum current 
they can carry indefinitely, thus allowing about twenty-five per cent overload 
before fuse melts. 


With naked open fuses, of ordinary shapes and not over 500 amperes capacity, the maxzmum cur- 
rent which will melt them in about five minutes may be safely taken as the melting point, as the fuse 
practically reaches its maximum temperature in this time. With larger fuses a longer time is 
necessary. 


Inclosed fuses where the fuse is often in contact with substances having good conductivity to heat 
and often of considerable volume, require a much longer time to reach a maximum temperature, on 
account of the surrounding material which heats up slowly. 

These data are given to facilitate testing. 


c. Fuse terminals must be stamped with the maker’s name, initials, or 
some known trade-mark, 


54. Cutout Cabinets — 


a. Must be so constructed, and cutouts so arranged, as to obviate any 
danger of the melted fuse metal coming in contact with any substance which 
might be ignited thereby. 


A suitable box can be made of marble, slate, or wood, strongly put together, the door to close 
against a rabbet so as to be perfectly dust-tight, and it should be hung on strong hinges, and held 
closed by a strong hook or catch. If the box is wood, the inside should be lined with sheets of asbestos 
board about one-sixteenth of an inch in thickness, neatly put on and firmly secured in place by shellac 
and tacks. The wire should enter through holes bushed with porcelain bushings; the bushings tightly 
fitting the holes in the box, and the wires tightly fitting the bushings (using tape to build up the wire, if 
necessary) so as to keep out the dust. 


55. Sockets — 
(See Vo. 27.) 


Sockets of all kinds, including wall receptacles, must be constructed in 
accordance with the following specifications : — 

a. STANDARD SIZES.— The standard lamp socket shall be suitable for 
use on any voltage not exceeding 250 and with any size lamp up to fifty candle- 
power. For lamps larger than fifty candle-power a standard keyless socket 
may be used, or if a key is required, a special socket designed for the current to 
be used must be made. Any special sockets must follow the general spirit of 
these specifications. 

6. MARKING. — The standard socket must be plainly marked fifty candle- 
power, 250 volts, and with either the manufacturer’s name or registered trade- 


476 ELECTRIC LICH TIING, 


- 


mark. Special large sockets must be marked with the current and voltage for 
which they are designed. 

c. SHELL.— Metal used for shells must be moderately hard, but not hard 
enough to be brittle or so soft as to be easily dented or knocked out of place. 
Brass shells must be at least 0.013 inch in thickness, and shells of any other 
material must be thick enough to give the same stiffness and strength of 
brass. 

d. LINING.— The inside of the shells must be lined with insulating 
_material, which shall absolutely prevent the shell from becoming a part of the 
circuit, even though the wires inside the socket should start from their position 
under. binding screws. 

The material used for lining must be at least one-thirty-second of an inch 
in thickness, and must be tough and tenacious. It must not be injuriously 
affected by the heat from the largest lamp permitted in the socket, and must 
leave the water in which it is boiled practically neutral. It must be so firmly 
secured to the shell that it will not fall out with ordinary handling of the socket. 
It is preferable to have the lining in one piece. 


e. Cap.— Caps when of sheet brass must be at least 0.013 inch in thickness, 
and when cast or made of other metals must be of equivalent strength. The 
inlet piece, except for special sockets, must be tapped and threaded for 
ordinary one-eighth-inch pipe. It must contain sufficient metal for a full, 
strong thread, and, when not of the same piece as the cap, must be joined to it 
in a way to give the strength of a single piece. 


There must be sufficient room in the cap to enable the ordinary wireman 
to easily and quickly make a knot in the cord and push it into place in cap 
without crowding. All parts of the cap upon which the knot is likely to bear 
must be smooth and well insulated. 


jf. FRAME AND SCREWS.— The frame holding moving parts | must be 
sufficiently heavy to give ample strength and stiffness. 

Brass pieces containing screw threads must be at least 0.06 of an inch in 
thickness. 

Binding post screws must not be smaller than No. 5 wire and about forty 
threads per inch, 

g. SPACING.— Points of opposite polarity must everywhere be kept not 
less than three-sixty-fourths of an inch apart unless separated by a reliable 
insulation, 

hk. CONNECTIONS.— The connecting points for the flexible cord must be 
made to very securely grip a No. 16 or 18 B. & S. conductor. A turned-up 
lug, arranged so that the cord may be gripped between the screw and the lug in 
such a way that it cannot possibly come out, is strongly advised. 

z. Lamp HOLDER.— The socket must firmly hold the lamp in place so that 
it cannot be easily jarred out, and must provide a contact good enough to pre- 
vent undue heating with maximum current allowed. The holding pieces, 
springs and the like, if a part of the circuit, must not be sufficiently exposed to 
allow them to be brought in contact with anything outside of lamp and 
socket. 

j. BASE.— The inside parts of the socket, which are of insulating material, 
except the lining, must be made of porcelain. 

&. KeEy.— The socket key-handle must be of such a material that it will 
not soften from the heat of a fifty candle-power lamp hanging downwards in. 


APPENDIX 1. ATT 


air at seventy degrees Fahrenheit from the socket, and must be securely, 
but not necessarily rigidly, attached to the metal spindle it is designed to 
turn. , . 

7. SEALING.—AIl screws in porcelain pieces, which can be firmly sealed 
in place, must be so sealed by a waterproof compound which will not melt 
below 200 degrees Fahrenheit. 

m. PUTTING TOGETHER, — The socket must, as a whole, be so put 
together that it will not rattle to pieces. Bayonet joints or equivalent are 
recommended. 

nz. TEST.— The socket when slowly turned “on and off,” at the rate of 
about two or three times per minute, must ‘‘make and break”’ the circuit 
6,000 times before failing, when carrying a load of one ampere at 220 volts. 

o. KEYLESS SOCKETS. — Keyless sockets of all kinds must comply with 
requirements for key sockets as far as they apply. 

p. SOCKETS OF INSULATING MATERIALS.— Sockets made of porcelain 
or other insulating material must conform to the above requirements as far as 
they apply, and all parts must be strong enough to withstand a moderate 
amount of hard usage without breaking. 

g. INLET BUSHING.— When the socket is not attached to fixtures the 
threaded inlet must be provided with a strong insulating bushing, having a 
smooth hole of at least fifteen-sixty-fourths of an inch in diameter. The 
corners of the bushing must be rounded and all inside fins removed, so that in 
no place will the cord be subjected to the cutting or wearing action of a sharp 
edge. 


56, Hanger-boards — 


a. Hanger-boards must be so constructed that all wires and current-carry- 
ing devices thereon shall be exposed to view, and thoroughly insulated by being 
mounted on a non-combustible, non-absorptive insulating substance. All 
switches attached to the same must be so constructed that they shall be 
automatic in their action, cutting off both poles to the lamp, not stopping 
between points when started, and preventing an arc between points under all 
circumstances. 


57, Arc Lamps — 
(For installation rules, see No, 19.) 


a. Must be provided with reliable stops to prevent carbons from falling 
out in case the clamps become loose. 

6. Must be carefully insulated from the circuit in all their exposed parts. 

c. Must, for constant-current systems, be provided with an approved hand 
switch, also an automatic switch that will shunt the current around the carbons, 
should they fail to feed properly. 

The hand switch to be approved, if placed anywhere except on the lamp 
itself, must comply with requirements for switches on hanger-boards as laid 
down in No. 56. 


58. Spark Arresters — 
(See /Vo. 19 c.) 


a. Spark arresters must so close the upper orifice of the globe that it will 
be impossible for any sparks thrown off by the carbons to escape. 


A478 ELECTRIC LIGHTING. 


59, Insulating Joints — 
(See Vo. 26 a.) 


a. Must be entirely made of material that will resist the action of illumi- 
nating gases, and will not give way or soften under the heat of an ordinary gas 
flame or leak under a moderate pressure. They shall be so arranged that a 
deposit of moisture will not destroy the insulating effect, and shall have an 
insulating resistance of at least 250,000 ohms between the gas-pipe attachments, 
and be sufficiently strong to resist the strain they will be liable to be subjected 
to in being installed. 

6. Insulating joints having soft rubber in their construction will not be — 
approved. 


60. Resistance Boxes and Equalizers — 
(For znstallation rules, see Vo. 4.) 


a. Must be equipped with metal, or with other non-combustible frames. 


The word ‘‘ frame ’’ in this section relates to the entire case and surroundings of the rheostat, and not 
alone to the upholding supports. 


61. Reactive Coils and Condensers — 


a. Reactive coils must be made of non-combustible material, mounted on 
non-combustible bases, and treated, in general, like sources of heat. 

6. Condensers must be treated like apparatus operating with equivalent 
voltage and currents. They must have non-combustible cases and supports, 
and must be isolated from all combustible materials, and, in general, treated 
like sources of heat. 


, 


62. Transformers — 
(For installation rules, see Nos. 11, 13, and 33.) 


a. Must not be placed in any but metallic or other non-combustible 
cases. 
6. Must be constructed to comply with the following tests: 


1. Shalf be run for eight consecutive hours at full load in watts under 
conditions of service, and at the end of that time the rise in tem- 
perature, as measured by the increase of resistance of the primary 
coil, shall not exceed 135 degrees Fahrenheit. 

2. The insulation of transformers when heated shall withstand continu- 
ously for five minutes a difference of potential of 10,000 volts 
(alternating) between primary and secondary coils and core, and 
between the primary coils and core and a no-load ‘“‘run”’ at double 
voltage for thirty minutes. 


63. Lightning Arresters — 
(For installation rules, See No. 5.) 


a. Must be mounted on non-combustible bases, and must be so constructed 
as not to maintain an arc after the discharge has passed, and must have no 
moving parts. 


APPENDIX I. 479 
CUASS. Lo 


MISCELLANEOUS. 


64. Signaling Systems (governing wiring for telephone, telegraph, district 
messenger, and call-bell circuits, fire and burglar alarms, and all similar 
systems) — 

a. Outside wires should be run in underground ducts or strung on poles 
and, as far as possible, kept off of buildings, and must not be placed on the 
same cross-arm with electric light or power wires. 

6. When outside wires are run on same pole with electric light or power 
wires, the distance between the two inside pins of each cross-arm must not be 
less than twenty-six inches. 

c. All aerial conductors and underground conductors which are directly 
connected to aerial wires must be provided with some approved protective de- 
vice, which shall be located as near their point of entrance to the building as 
possible, and not less than six inches from curtains or other inflammable 
material. 

d@. If the protector is placed inside of building, wires, from outside sup- 
port to binding-posts of protector, shall comply with the following require- 
ments: 

Must be of copper, and not smaller than No. 16 B. & S. gauge. 


Must have an approved rubber insulating covering (see No. 41). 
Must have drip loops in each wire immediately outside the building. 


ees a 


Must enter buildings through separate holes sloping upward from the 
outside ; when practicable, holes to be bushed with non-absorptive, 
non-combustible insulating tubes extending through their entire 
length. Where tubing is not practicable, the wires shall be wrapped 
with two layers of insulating tape. 


5. Must be supported on porcelain insulators, so that they will not come 
in contact with anything other than their designed supports. 


6. A separation between wires of at least two and one-half inches must 
be maintained. 


In case of crosses these wires may become a part of a high-voltage circuit, so that similar care to 
that given high-voltage circuits is needed in placing them. Reliable porcelain bushings at the entrance 
holes are desirable, and are only waived under adverse conditions, because the state of the art in this 
type of wiring makes an absolute requirement inadvisable. 


e. The ground wire of the protective device shall be run in accordance 
with the following requirements : 


1, Shall be of copper, and not smaller than No. 16 B. & S. 
2. Must have an approved rubber insulating covering (see No. 41). 


3. Shall run in as straight a line as possible to a good permanent 
ground, to be made by connecting to water- or gas-pipe, preferably 
water-pipe. If gas-pipe is used, the connection, in all cases, must 
be made between the meter and service pipes. In the absence of 
other good ground, the ground shall be made by means of a metallic 
plate or bunch of wires buried in permanently moist earth. 


AS0 ELECTRIC LIGHTING. 
4. Shall be kept at least three inches from all other conductors and sup- 
ported on porcelain insulators, so as not to come in contact with 
anything other than its designed supports. 


In attaching a ground wire to a pipe, it is often difficult to make a thoroughly reliable solder joint. 
It is better, therefore, where possible, to carefully solder the wire to a brass plug, which may then be 
firmly screwed into a pipe fitting. 

Where such joints are made under ground, they should be thoroughly painted and taped to prevent 


corrosion. 


jf. The protector to be approved must comply with the following require- 
ments: 

1, Must be mounted on non-combustible, non-absorptive insulating 
bases, so designed that when the protector is in place, all parts 
which may be alive will be thoroughly insulated from the wall hold- 
ing the protector. 


2. Must have the following parts: 

A lightning arrester which will operate with a difference of potential 
between wires of not over 500 volts, and so arranged that the 
chance of accidental grounding is reduced to a minimum. 

A fuse designed to open the circuit in case the wires become crossed 
with light or power circuits. The fuse must be able to open the 
circuit without arcing or serious flashing when crossed with any 
ordinary commercial light or power circuit. 

A heat coil which will operate before a sneak current can damage 
the instrument the protector is guarding. 


The heat coil is designed to warm up and melt out with a current large enough to endanger 
the instruments if continued for a long time, but so small that it would not blow the fuses 
ordinarily found necessary for such instruments. These smaller currents are often called 
“sneak ’’ currents. 


3. The fuses must be so placed as to protect the arrester and heat coils, 


and the protector terminals must be plainly marked “line,” “ in- 
strument,” ‘ ground.” 


g. Wires beyond the protector, except where bunched, must be neatly 
arranged and securely fastened in place in any convenient, workmanlike man- 
ner. They must not come nearer than six inches to any electric light or power 
wire in the building, unless incased in approved tubing so secured as to pre- 
vent its slipping out of place. 


The wires would ordinarily be insulated, but the kind of insulation is not specified, as the pro- 
tector is relied upon to stop all dangerous currents. Porcelain tubing or circular loom conduit may be 
used for incasing wires where required as above. 


h. Wires connected with outside circuits, where bunched together within 
any building, or inside wires, where laid in conduits or ducts, with electric light 
or power wires, must have fire-resisting coverings, or else must be inclosed in 
an air-tight tube or duct. 


It is feared that if a burnable insulation were used, a chance spark might ignite it and cause a 
serious fire, for many installations contain a large amount of very readily burnable matter. 


65, Electric Gas Lighting — 
Where electric gas lighting is to be used on the same fixture with the 
electric light: 


APPENDIX I. 481 


a. No part of the gas-piping or fixture shall be in electric connection with 
the gas-lighting circuit. 

6. The wires used with the fixtures must have a non-inflammable insula- 
tion, or, where concealed between the pipe and shell of the fixture, the insula- 
tion must be such as required for fixture wiring for the electric light. 

c. The whole installation must test free from ‘“ grounds.” 

ad. The two installations must test perfectly free from connection with 
each other. 


66. Insulation Resistance — 


The wiring in any building rust test free from grounds; i.e., the com- 
plete installation must have an insulation between conductors and between 
all conductors and the ground (not including attachments, sockets, recep- 
ticles, etc.) of not less than the following: 


Up to 5 amperes. ... . . . 4,000,000 ohms. 
ae 10 < a Sarna ess ee 25000000 Fa 
we 25 SC oe SO it stem ys CO0-000 mon" 
WY 50 Me ees oe eey 2 £00000: 7 4° 
100 ie Se eee ee oe 2000004)" fe 
ch 200 s Ro. igo ae Me A 100,000 ‘* 
ne 400 es Paes so bee eh oe Oe 25,000 ‘* 
ce 800 oe Rein i eee oe 25,000 ‘* 
2Y 1,600 : yah LAY Werf \ Gera: 12,500 ‘ 


All cutouts and safety devices in place in the above. 
Where lamp sockets, receptacles, and electroliers, etc., are connected, one- 
half of the above will be required. 


67. Soldering Fluid — 


a. The following formula for soldering fluid is suggested : 


Saturated solution of zinc chloride . ... . . 5 parts 

INGO Ge G4 ae es 8 See on ye Bae era 

Glycerinet waar) Be eute bet ee a ee cee part 
CLASsSer. 


MARINE WORK. 


68. Generators — 


a. Must be located in a dry place. 

6. Must have their frames insulated from their bed-plates. 

c. Must each be provided with a waterproof cover. 

d. Must each be provided with a name-plate, giving the maker’s name, the 
capacity in voltage and amperes and normal speed in revolutions per minute. 


69. Wires — 
a. Must have an approved insulating covering. 


482 ELECTRIC LIGHTING. 


The insulation for all conductors, except for portables, to be approved, must be at least one- 
eighth-inch in thickness and be covered with a substantial waterproof and flameproof braid. The 
physical characteristics shall not be affected by any change in temperature up to 200 degrees Fahrenheit. 
After two weeks’ submersion in salt water at seventy degrees Fahrenheit it must show an insulation 
resistance of one megohm per mile after three minutes’ electrification, with 550 volts. 


6. Must have no single wire larger than No. 12 B. & S. Wires to be 
stranded when greater carrying capacity is required. No single solid wire 
smaller than No. 14 B. & S., except in fixture wiring, to be used. 


Stranded wires must be soldered before being fastened under clamps or binding screws, and when 
they have a conductivity greater than No. 10 B. & S. copper wire they must be soldered into lugs. 


c. Must be supported in approved molding, except at switch boards and 
portables. 


Special permission may be given for deviation from this rule in dynamo-rooms. 


d@. Must be bushed with hard-rubber tubing one-eighth of an inch in 
thickness when passing through beams and non-water-tight bulkheads. 

e. Must have, when passing through water-tight bulkheads and through all 
decks, a metallic stuffing tube lined with hard rubber. In case of deck tubes 
they shall be boxed near deck to prevent mechanical injury. 

fy. Splices or taps in conductors must be avoided as far as possible. Where 
it is necessary to make them they must be so spliced or joined as to be both 
mechanically and electrically secure without solder. They must then be sol- 
dered, to insure preservation, covered with an insulating compound equal to 
the insulation of the wire, and further protected by a waterproof tape. The 
joint must then be coated or painted with a waterproof compound. 


70, Portable Conductors — 


a. Must be made of two stranded conductors, each having a carrying 
capacity equivalent to not less than No. 14 B. & S. wire, and each covered with 
an approved insulation and covering. 


Where not exposed to moisture or severe mechanical injury, each stranded conductor must have a 
solid insulation at least one-thirty-second of an inch in thickness, and must show an insulation resistance 
between conductors, and between either conductor and the ground, of at least one megohm per mile 
after one week’s submersion in water at seventy degrees Fahrenheit and after three minutes’ electrifica- 
tion, with 590 volts, and be protected by a slow-burning, tough-braided outer covering. 

Where exposed to moisture and mechanical injury —as for use on decks, holds, and fire-rooms — 
each stranded conductor shall have a solid insulation to be approved, of at least one thirty-second of an 
inch in thickness and protected by a tough braid. The two conductors shall then be stranded together, 
using a jute filling. The whole shall then be covered with a layer of flax, either woven or braided, at 
least one-thirty-second of an inch in thickness, and treated with a non-inflammable waterproof compound. 
After one week’s submersion in water at seventy degrees Fahrenheit, at 5s0 volts and a three minutes’ 
electrification, must show an insulation between the two conductors, or between either conductor and 
the ground, of one megohm per mile. 


71. Bell or Other Wires — 


a. Shall never run in same duct with lighting or power wires. 


72. Table of Capacity of Wires — 


APPENDIX I. 483 


B. & &. G. Area Actual C. M. penis EE a es Amperes. 
19 1,288 rae ae ate 
18 1,624 ae ee 3 
17 2,048 Hes es aie 
16 2,583 es aie 6 
15 3,257 io i ee 
14 4,107 iA ae 12 
12 6,530 < es 17 

9.016 7 19 21 

11,368 7 18 25 

ae 14,336 e 17 30 
se 18,081 7 16 35 
ane 22,799 if 15 40 
AC 30,856 19 18 50 
ae 38,912 19 17 60 
is 49,077 19 16 70 
ac 60,088 37 18 85 
ae 75,776 37 17 100 
-, 99,064 61 18 120 
ne 124,928 61 17 145 
- 157,563 61 16 170 
198,677 61 15 200 

250,527 61 14 235 

296,387 91 15 270 

oe 373,737 91 14 320 
ae 412,639 127 15 340 


When greater conducting area than that of a single wire is required, the conductor shall be 
stranded in a series of 7, 19, 37, 61, 91, or 127 wires, as may be required ; the strand consisting of one cen- 
tral wire, the remainder laid around it concentrically, each layer to be twisted in the opposite direction 
from the preceding. 


73. Switchboards — ~ 


a. Must be made of non-combustible, non-absorptive insulating material, 
such as marble or slate. 

6. Must be kept free from moisture, and must be located so as to be acces- 
sible from all sides. 

c. Must have a main switch, main cutout and ammeter for each generator. 

Must also have a voltmeter and ground detector. 

d. Must have a cutout and switch for each side of each circuit leading 
from board. 


74. Resistance Boxes — 


a. Must be made of non-combustible material. 

6. Must be located on switchboard or away from combustible material. 
When not placed on switchboard they must be mounted on non-inflammable, 
non-absorptive insulating material. 

c. Must be so constructed as to allow sufficient ventilation for the uses to 
which they are put. 


75. Switches — 


a. Must have non-combustible, non-absorptive insulating bases. 
6. Must operate successfully at fifty per cent overload in amperes with 
twenty-five per cent excess voltage under the most severe conditions they are 


484 ELECTRICLIGH TING 


liable to meet with in practice, and must be plainly marked, where they will 
always be visible, with the name of the maker and the current and voltage for 
which the switch is designed.. 

c. Must be double pole when circuits which they control supply more than 
six sixteen-candle-power lamps or their equivalent. 


d. When exposed to dampness, they must be inclosed in a water-tight 
case. 


76. Cutouts — 


a. Must have non-combustible, non-absorptive insulating bases. 

6. Must operate successfully, under the most severe conditions they are 
liable to meet with in practice, on short circuit with fuse rated at fifty per cent 
above, and with a voltage twenty-five per cent above the current and voltage 
they are designed for, and must be plainly marked, where they will always be 
visible, with the name of the maker and current and voltage for which the 
device is designed. 

c. Must be placed at every point where a change is made in the size of 
the wire (unless the cutout in the larger wire will protect the smaller). 

@. In places such as upper decks, holds, cargo spaces, and fire-rooms a 
water-tight and fireproof cutout may be used, connecting directly to mains 
when such cutout supplies circuits requiring not more than 660 watts energy. 

e. When placed anywhere except on switchboards and certain places, as 
cargo spaces, holds, fire-rooms, etc., where it is impossible to run from center 
of distribution, they shall be in a cabinet lined with fire-resisting material. 

Ff. Except for motors, searchlights, and diving-lamps shall be so placed 
that no group of lamps, requiring a current of more than six amperes, shall 
ultimately be dependent upon one cutout. 


A single-pole covered cutout may be placed in the molding when same contains conductor sup- 
plying circuits requiring not more than 220 watts energy. 


77. Fixtures — 


a. Shall be mounted on blocks made from well-seasoned lumber treated 
with two coats of white lead or shellac. 

6. Where exposed to dampness, the lamp must be surrounded by a vapor- 
proof globe. 

c. Where exposed to mechanical injury, the lamp must be surrounded by 
a globe protected by a stout wire guard. 

@. Shall be wired with same grade of insulation as portable conductors 
which are not exposed to moisture or mechanical injury. 


78. Sockets — 


a. No portion of the lamp socket or lamp base exposed to contact with 
outside objects shall be allowed to come into electrical contact with either of 
the conductors. 


79. Wooden Moldings — 


a. Must be made of well-seasoned lumber, and be treated inside and out 
with at least two coats of white lead or shellac. 

6. Must be made of two pieces, a backing and a capping, so constructed 
as to thoroughly incase the wire, and provide a one-half inch tongue between 
the conductors, and a solid backing which, under grooves, shall not be less 
than three-eighths of an inch in thickness. 


APPENDIX 1. 485 


c. Where molding is run over rivets, beams, etc.,a backing strip must 
first be put up and the molding secured to this. 
ad. Capping must be secured by brass screws. 


80. Motors — 


a. Must be wired under the same precautions as with a current of same 
volume and potential for lighting. The motor and resistance box must be 
protected by a double-pole cutout, and controlled by a double-pole switch, 
except in cases where one-quarter horse-power or less is used. 


‘The leads or branch circuits should be designed to carry a current at least fifty per cent greater than 
that required by the rated capacity of the motor to provide for the inevitable overloading of the motor 


at times. 

6. Must be thoroughly insulated. Where possible, should be set on base 
frames made from filled, hard, dry wood, and raised above surrounding deck. 
On hoists and winches they shall be insulated from bed-plates by hard rubber, 
fiber, or similar insulating material. 

c. Shall be covered with a waterproof cover when not in use. 

ad. Must each be provided with a name-plate giving maker’s name, the 
capacity in volts and amperes, and the normal speed in revolutions per minute. 


GENERAL SUGGESTIONS. 


In all electric work conductors, however well insulated, should always be 
treated as bare, to the end that under no conditions, existing or likely to exist, 
can a grounding or short circuit occur, and so that all leakage from conductor 
to conductor, or between conductor and ground, may be reduced to the 
minimum, : 

In all wiring special attention must be paid to the mechanical execution of 
the work. Careful and neat running, connecting, soldering, taping of conduc- 
tors and securing and attaching of fittings, are specially conducive to security 
and efficiency, and will be strongly insisted on. 

In laying out an installation, except for constant-current systems, the work 
should, if possible, be started from a center of distribution, and the switches 
and cutouts, controlling and connected with the several branches, be grouped 
together in a safe and easily accessible place, where they can be readily got at 
for attention or repairs. The load should be divided as evenly as possible 
among the branches, and all complicated and unnecessary wiring avoided. 

The use of wire-ways for rendering concealed wiring permanently access- 
ible is most heartily indorsed and recommended ; and this method of accessible 
concealed construction is advised for general use. 

Architects are urged, when drawing plans and specifications, to make pro- 
vision for the channeling and pocketing of buildings for electric light or 
power wires, and in specifications for electric gas lighting to require a two-wire 
circuit, whether the building is to be wired for electric lighting or not, so that 


no part of the gas fixtures or gas-piping be allowed to be used for the gas- 
lighting circuit. 


HN ed ed in D) ic INE 


REPORT OF THE COMMITTEE ON 
STANDARDIZATION. 


[Accepted by the INSTITUTE, June 26, 1899.] 


To the Council of The AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS. 

Gentlemen: 

Your committee on Standardization begs to submit the following report, 
covering such subjects as have been deemed of pressing and immediate impor- 
tance, and which are of such a nature that general agreement may be expected 
upon them. 

While it is the opinion of the committee that many other matters might 
advantageously have been considered, as, for example, standard methods of 
testing: yet it has been deemed inexpedient to attempt to cover in a single 
report more than is here submitted. 

Yours respectfully, 
FRANCIS B. CROCKER, Chairman. 
CARY T. HUTCHINSON. 
A. E. KENNELLY. 
JOHN W. LIEB, Jr. 
CHARLES P. STEINMETZ. 
LEWIS B. STILLWELL. 
ELIHU THOMSON. 


GENERAL PLAN, 


Efficiency. Sections 1 to 24 

(I) Commutating Machines, Sections 6 to 11 
(11) Synchronous Machines, - 10 to 11 
(111) Synchronous Commutating Machines, : 12 to 15 
(IV) Rectifying Machines, a 16 to 17 
(V) Stationary Induction Apparatus, fh 18 to 19 
(VI) Rotary Induction Apparatus, m 20 to 23 
(VII) Transmission Lines, : 24 


Rise of Temperature. Sections 25 to 31. 

Insulation. Sections 32 to 41. 

Regulation. Sections 42 to 61. 

Variation and Pulsation. Sections 62 to 65, 

Rating. Sections 66 to 73. 

Classification of Voltages and Frequencies. Sections 74 to 78. 
Overload Capacities. Sections 79 to 82. 


Appendices. (1) Efficiency. 
(II) Apparent Efficiency. 
(III) Power Factor and Inductance Factor. 
(IV) Notation. 
(V) Table of Sparking Distances. 


486 


APPENDIX I. 487 


Electrical Apparatus will be treated under the following heads : — 


I. Commutating Machines, which comprise a constant magnetic field, a 
closed-coil armature, and a multi-segmental commutator connected thereto. 

Under this head may be classed the following: Direct-current generators ; 
direct-current motors ; direct-current boosters; motor-generators ; dynamotors; 
converters and closed-coil arc machines. 

A booster is a machine inserted in series in a circuit to change its voltage, 
and may be driven either by an electric motor, or otherwise. In the former 
case it is a motor-booster. 

A motor-generator is a transforming device consisting of two machines; 
a motor and a generator, mechanically connected together. 

A dynamotor is a transforming device combining both motor and gene- 
rator action in one magnetic field, with two armatures or with an armature 
having two separate windings. 


For converters, see III. 


II. Synchronous Machines, which comprise a constant magnetic field, and 
an armature receiving or delivering alternating currents in synchronism with 
the motion of the machine; z. ¢., having a frequency equal to the product of 
the number of pairs of poles and the speed of the machine in revolutions per 


second. 


III. Synchronous Commutating Machines: — These include: 1. Synchron- 
ous converters: i.e., converters from alternating to direct, or from direct to 
alternating current, and 2. Double-current generators; i.e., generators pro- 
ducing both direct and and alternating currents. 

A converter is a rotary device transforming electric energy from one form 
into another without passing it through the intermediary form of mechanical 
energy. 

A converter may be either: 

a. A direct-current converter, converting from a direct current to a direct 
current or 

6. A synchronous converter, formerly called a rotary converter, convert- 
ing from an alternating to a direct current, or vice versa. 

Phase converters are converters from an alternating-current system to an 
alternating-current system of the same frequency but different phase. 

Frequency converters are converters from an alternating-current system of 
one frequency to an alternating-current system of another frequency, with or 
without changes of phase. 


IV. Rectifying Machines, or Pulsating-Current-Generators, which produce a 
unidirectional current of periodically varying strength. 


V. Stationary Induction Apparatus: i.e., stationary apparatus changing 
electric energy from one form into another, without passing it through an 
intermediary form of energy. These comprise: 

a. Transformers, or stationary induction apparatus in which the primary 
and secondary windings are electrically insulated from each other. 

6. Auto-transformers, formerly called compensators: i.e., stationary induc- 
tion apparatus in which part of the primary winding is used as a secondary 
winding, or conversely. 

c. Potential regulators, or stationary induction apparatus having a coil 


488 ELECTRIC THICHPING. 


in shunt, and a coil in series with the circuit, so arranged that the ratio of 
transformation between them is variable at will. 

These may be divided into: — 

1. Compensator potential-regulators, in which the number of turns of 
one of the coils is changed. 

2. Induction potential-regulators, in which the relative positions of pri- 
mary and secondary coils is changed. 

5. Magneto potential-regulators, in which the direction of the magnetic 
flux with respect to the coils is changed. 

ad. Reactive coils, or reactance coils, formerly called choking coils: i.e., 
stationary induction apparatus. used to produce impedance or phase dis- 
placement. 

VI. Rotary Induction Apparatus, which consists of primary and secondary 
windings rotating with respect to each other, They comprise: — 

a. Induction motors. 

6. Induction generators. 

c. Frequency changers. 

d@. Rotary phase converters. 


EFFICIENCY. 


1. The “efficiency ” of an apparatus is the ratio of its net power output 
to its gross power input.* 

_2. Electric power should be measured at the terminals of the apparatus. 

3. In determining the efficiency of alternating-current apparatus, the elec- 
tric power should be measured when the current is in phase with the Z.AZF., 
unless otherwise specified, except when a definite phase difference is inherent 
in the apparatus, as in induction motors, etc. 

4. Mechanical power in machines should be measured at the pulley, 
gearing, coupling, etc., thus excluding the loss of power in said pulley, gear- 
ing, or coupling, but including the bearing friction and windage. The magni- 
tude of bearing friction and windage may be considered as independent of 
the load. The loss of power in the belt and the increase of bearing friction 
due to belt tension, should be excluded. Where, however, a machine is 
mounted upon the shaft of a prime mover, in such a manner that it cannot 
be separated therefrom, the frictional losses in bearings and in windage, which 
ought, by definition, to be included in determining the efficiency, should be 
excluded, owing to the practical impossibility of determining them satisfac- 
torily. The brush friction, however, should be included. 

a. Where a machine has auxiliary apparatus, such as an exciter, the 
power lost in the auxiliary apparatus shou'd not be charged to the machine, 
but to the plant consisting of machine and auxiliary apparatus taken together, 
The plant efficiency in such cases should be distinguished from the machine 
efficiency. 

5. The efficiency may be determined by measuring all the losses individ- 
ually and adding their sum to the output to derive the input, or subtract- 
ing their sum from the input to derive the output. All losses should be 
measured at, or reduced to, the temperature assumed in continuous operation, 
or in operation under conditions specified. (See Sections 25 to 31.) 


* An exception should be noted in the case of storage batteries or apparatus for storing energy, 
in which the efficiency, unless otherwise qualified, should be understood as the ratio of the energy 
output to the energy intake in a normal cycle. 


APPENDIX Il. 489 


In order to consider the application of the foregoing rules to various 
machines in general use, the latter may be conveniently divided into classes 
as follows : — 


I. Commutating Machines. — 


6. In commutating machines the losses are: — 

a. Bearing friction and windage. (See Section 4.) 

6. Molecular magnetic friction, and eddy currents in iron and copper. 
These losses should be determined with the machine on open circuit, and at a 
voltage equal to the rated voltaze + 7y in a generator, and — /y in a motor, 
where / denotes the current strength, and 7 denotes the internal resistance 
of ‘the machine. They should be measured at the correct speed and voltage, 
since they do not usually vary in proportion to the speed or to any definite 
power of the voltage. 

c. Armature resistance losses, /? 7’, where / is the current strength in the 
armature, and 7’ is the resistance between armature brushes, excluding the 
resistance of brushes and brush contacts. 

@. Commutator brush friction. 

e. Commutator brush-coatact resistance. It is desirable to point out that 
with carbon brushes the losses (@) and (é) are usually considerable in low- 
voltage machines. 

fy Field excitation. With separately excited fields, the loss of power in 
the resistance of the field coils alone should be considered. With shunt fields 
or series fields, however, the loss of power in the accompanying rheostat 
should also be included, the said rheostat being considered as an essential part 
of the machine, and not as separate auxiliary apparatus. 

(0) and (c) are losses in the armature or ‘‘armature losses ;” (@) and (e) 
“commutator losses ;” (f) ‘field losses.” 

7. The difference between the total losses under load and the sum of the 
losses above specified, should be considered as ‘“‘load losses” and are usu- 
ally trivial in commutating machines of small field distortion. When the 
field distortion is large, as is shown by the necessity for shifting the brushes 
between no load and full load, or with variations of load, these load losses may 
be considerable, and should be taken into account. In this case the efficiency 
may be determined either by input and output measurements, or the load 
losses may be estimated by the method of Section II. 

8. Boosters should be considered and treated like other direct-current 
machines in regard to losses. 

9. In motor-generators, dynamotors, or converters, the efficiency is the 
electric output 
electric input. 


Il. Synchronous Machines. — 


10. In synchronous machines the output or input should be measured 
with the current tn phase with the terminal “.47./., except when otherwise 
expressly specified. 

Owing to the uncertainty necessarily involved in the approximation of 
load losses, it is preferable, whenever possible, to determine the efficiency of 
synchronous machines, by input and output tests. 

11. The losses in synchronous machines are: 

a. Bearing friction and windage. (See Section 4.) 


490 FLECTRIC LIGHTING. 


- 


6. Molecular magnetic friction and eddy currents in iron, copper, and 
other metallic parts. These losses should be determined at open circuit of 
the machine at the rated speed and at the rated voltage, + 7/7 in a syn- 
chronous generator, —/7 in a synchronous motor, where / = current in arma- 
ture, 7 = armature resistance. It is undesirable to compute these losses from 
observations made at other speeds or voltages. 

These losses may be determined either by driving the machine by a motor, 
or by running it as a synchronous motor, and adjusting its fields so as to 
get minimum current input and measuring the input by wattmeter. The 
former is the preferable method, and in polyphase machines the latter method 
is liable to give erroneous results in consequence of unequal distribution of 
currents in the different circuits caused by inequalities of the impedance of 
connecting leads, etc. 

c. Armature-resistance loss, which may be expressed by # /?7; where 
vy =resistance of one armature circuit or branch, 7/=the current in such 
armature circuit or branch, and =the number of armature circuits or 
branches. 

ad. Load losses as defined in Section 7. While these losses cannot well 
be determined individually, they may be considerable and, therefore, their 
joint influence should be determined by observation. This can be done by 
operating the machine on short circuit and at full-load current, that is, by de- 
termining what may be called the ‘short-circuit core loss.’”’ With the low 
field intensity and great lag of current existing in this case, the load losses are 
usually greatly exaggerated. 

One-third of the short-circuit core loss may, as an approximation, and in 
the absence of more accurate information, be assumed as the load loss. 

e. Collector-ring friction and contact resistance. These are generally 
negligible, except in machines of extremely low voltage. 

fj. Field excitation. In separately-excited machines, the 7? 7 of the field 
coils proper should be used. In self-exciting machines, however, the loss in 
the field rheostat should be included. (See Section 6/.) 


III. Synchronous Commutating Machines. — 


12. In synchronous converters, the power of the alternating-current side 
is to be measured with the current in phase with the terminal &.A7./., unless 
otherwise specified. | 

13. In double-current generators, the efficiency of the machine should be 
determined as a direct-current generator in accordance with Section 6, and 
as an alternating-current generator in accordance with Section 11. The two 
values of efficiency may be different, and should be clearly distinguished. 

14. In synchronous converters the losses should be determined when 
driving the machine by a motor. These losses are: — 

a. Bearing friction and windage. (See Section 4.) 

ce. Molecular magnetic friction and eddy currents in. iron, copper, and 
metallic parts. These losses should be determined at open circuit and at the 
rated terminal voltage, no allowance being made for the armature resistance, 
since the alternating and the direct currents flow in opposite directions. 

c. Armature resistance. The loss in the armature is g /27, where 7/= 
direct current in armature, » = armature resistance, and g a factor which is 
equal to 1.37 in single-phasers, 0.56 in three-phasers, 0.87 in quarter-phasers 
and 0.26 in six-phasers. 


APPENDIX II. 491 


ad. Load losses. The load losses should be determined in the same 
manner as described in Section 11 d@., with reference to the direct-current side. 

e and f. Losses in commutator and collector friction and brush-contact 
resistances, (pee oections 6 and 11)) 

g. Field excitation. In separately-excited fields, the 7? 7 loss in the field 
coils proper should be taken, while in shunt and series fields the rheostat 
loss should be included, except where fields and rheostats are intentionally 
modified to produce effects outside of the conversion of electric power, as for 
producing phase displacement for voltage control. In this case 25 per cent 
of the 7/27 loss in the field proper at non-inductive alternating circuit should 
be added as proper estimated allowance for normal rheostat losses. (See 
Section 6/.) 

15. Where two similar synchronous machines are available, their efficiency 
can be determined by operating one machine as a converter from direct to 
alternating, and the other as a converter from alternating to direct, connecting 
the alternating sides together, and measuring the difference between the direct- 
current input and the direct-current output. This process may be modified by 
returning the output of the second machine through two boosters into the first 
machine and measuring the losses. Another modification might be to supply 
the losses by an alternator between the two machines, using potential regu- 
lators. 

IV. Rectifying Machines or Pulsating-Current Generators. — 

16. These include: Open-coil arc machines, constant-current rectifiers, 
constant-potential rectifiers. 

The losses in open-coil arc machines are essentially the same as in Sec- 
tions 6 to 9 (closed-coil commutating machines.) In alternating-current recti- 
fiers, however, the output must be measured by wattmeter and not by volt- 
meter and ammeter, since, owing to the pulsation of current and #.47.F.,a 
considerable discrepancy may exist between watts and volt amperes, amount- 
ing to as much as 10 or 15 per cent. 

17. In constant-current rectifiers, transforming from constant-potential 
alternating to constant direct current by means of constant-current trans- 
formers and rectifying commutators, the losses in the transformers are to be 
included in the efficiency, and have to be measured when operating the recti- 
fier, since in this case the losses are generally greater than when feeding an 
alternating secondary circuit. In constant-current transformers the load 
losses are usually larger than in constant-potential transformers, and thus 
should not be neglected. 

The most satisfactory method of determining the efficiency in rectifiers 
is to measure electric input and electric output by wattmeter. The input is 
usually not non-inductive, owing to a considerable phase displacement and to 
wave distortion. For this reason the apparent efficiency should also be con- 
sidered, since it is usually much lower than the true efficiency. The power 
consumed by the synchronous motor or other source driving the rectifier 
sbould be included in the electric input. 


4 


V. Stationary Induction Apparatus. — 


18. Since the efficiency of induction apparatus depends upon the wave 
shape of -.1/./., it should be referred to a sine wave of £.17.F., except 


492 ELACTRIGC. LIGHHING 


expressly specified otherwise. The efficiency should be measured with non- 
inductive load, and at rated frequency, except where expressly specified other- 
wise. The losses are: 


a. Molecular magnetic friction and eddy currents measured at open cir- 
cuit and at rated voltage — /7, where /=rated current, y= resistance of 
primary circuit. 

6. Resistance losses, the sum of the 727 of primary and of secondary in 
a transformer, or of the two sections of the coil in the compensator or auto- 
transformer, where / = current in the coil or section of coil, 7 = resistance. 


c. Load losses, i.e., eddy currents in the iron and especially in the copper 
conductors, caused by the current. They should be measured by short-cir- 
cuiting the secondary of the transformer and impressing upon the primary an 
£.M F., sufficient to send full-load current through the transformer. The loss 
in the transformer under these conditions measured by wattmeter gives the 
load losses + 7? 7 losses in both primary and secondary coils. 


d. Losses due to the methods of cooling, as power consumed by the 
blower in air-blast transformers, and power consumed by the motor driving 
pumps in oil or water cooled transformers. Where the same cooling appara- 
tus supplies a number of transformers, or is installed to supply future addi- 
tions, allowance should be made therefor. 


19. In potential regulators the efficiency should be taken at the maximum 
voltage for which the apparatus is designed, and with non-inductive load, 
unless otherwise specified. 


VI. Rotary Induction Apparatus. — 


20. Owing to the existence of load losses and since the magnetic density 
in the induction motor under load changes in a complex manner, the efficiency 
should be determined by measuring the electric input by wattmeter and the 
mechanical output at the pulley, gear, coupling, etc. 


21. The efficiency should be determined at the rated frequency and the 
input measured with sine waves of impressed £.4Z.F. 


22. The efficiency may be calculated from the apparent input, the power 
factor, and the power output. The same applies to induction generators. 
Since phase displacement is inherent in induction. machines, their apparent 
efficiency is also important. 


23. In frequency changers; i.e., apparatus transforming from a polyphase 
system to an alternating system of different frequency, with or without a 
change in the number of phases, and phase converters; i.e., apparatus convert- 
ing from an alternating system, usually single phase, to another alternating sys- 
tem, usually polyphase, of the same frequency, the efficiency should also be 
determined by measuring both output and input. 


o~ 


VII. Transmission Lines. — 


24. The efficiency of transmission lines should be measured with non- 
inductive load at the receiving end, with the rated receiving pressure and fre- 
quency, also with sinusoidal impressed /.//. /.’s., except where expressly 
specified otherwise, and with the exclusion of transformers or other apparatus 
at the ends of the line. 


APPENDIX II. 493 


RISE, OF. TEMPERATURE, 
General Principles. — 


25. Under regular service conditions, the temperature of electrical 
machinery should never be allowed to remain at a point at which permanent 
deterioration of its insulating material takes place. 


26. The rise of temperature should be referred to the standard conditions 
of a room-temperature of 25° C., a barometric pressure of 760 mm. and normal 
conditions of ventilation; that is, the apparatus under test should neither be 
exposed to draught nor inclosed, except where expressly specified. 


27. If the room temperature during the test differs from 25° C., the ob- 
served rise of temperature should be corrected by = per cent for each degree 
C.* Thus with a room temperature of 35° C., the observed rise of temperature 
has to be decreased by 4 per cent, and with a room temperature of 15° C., the 
observed rise of temperature has to be increased by 5 per cent. The ther- 
mometer indicating the room temperature should be screened from thermal 
radiation emitted by heated bodies, or from draughts of air. When it is im- 
practicable to secure normal conditions of ventilation on account of an adja- 
cent engine, or other sources of heat, the thermometer for measuring the air 
temperature should be placed so as fairly to indicate the temperature which 
the machine would have if it were idle, in order that the rise of temperature 
determined shall be that caused by the operation of the machine. 


28. The temperature should be measured after a run of sufficient duration 
to reach practical constancy. This is usually from 6 to 18 hours, according to 
the size and construction of the apparatus. It is permissible, however, to 
shorten the time of the test by running a lesser time on an overload in current 
and voltage, then reducing the load to normal, and maintaining it thus until 
the temperature has become constant. 

In apparatus intended for intermittent service, as railway motors, starting 
rheostats, etc., the rise of temperature should be measured after a shorter time, 
depending upon the nature of the service, and should be specified. 


In apparatus which by the nature of their service may be exposed to over- 
load, as railway converters, and in very high voltage circuits, a smaller rise of 
temperature should be specified than in apparatus not liable to overloads or in 
low voltage apparatus. In apparatus built for conditions of limited space, as 
railway motors, a higher rise of temperature must be allowed. 


29. In electrical conductors, the rise of temperature should be determined 
by their increase of resistance. For this purpose the resistance may be meas- 
ured either by galvanometer test, or by drop-of-potential method. A tem- 
perature coefficient of 0.4 per cent per degree C. may be assumed for copper.t 
Temperature elevations measured in this way are usually in excess of tem- 
perature elevations measured by thermometers. 


30. It is recommended that the following maximum values of temperature 
elevation should not be exceeded: 


* This correction is also intended to compensate, as nearly as is at present practicable, for the 
error involved in the assumption of a constant temperature coefficient of resistivity ;i.e., o.4 per cent 
degree C. taken with varying initial temperatures. 


+ By the formula R=, (1 +0.0049). Where Bs is the resistance at room temperature, A, the 
resistance when heated, and @ the temperature elevation (7 —7) in degrees centigrade. 


494 BLRCTRICWIGHTIVG. 


Commutating machines, rectifying machines, and synchronous machines. 
Field and armature, by resistance, 50° C, 
Commutator and collector rings and brushes, by thermometer, 55° C, 
Bearings and other parts of machine, by thermometer, 40° C, 

Rotary induction apparatus: 
Electric circuits, 50° C., by resistance. 
Bearings and other parts of the machine, 40° C., by thermometer. 

In squirrel-cage or short-circuited armatures, 55° C., by thermometer, may 
be allowed. 

Transformers for continuous service — electric circuits by resistance, 50° C., 
other parts by thermometer, 40° C., under conditions of normal ventilation. 

Reactive coils, induction and magneto regulators -— electric circuits by 
resistance, 55° C., other parts by thermometer, 45° C. 

Where a thermometer, applied to a coil or winding, indicates a higher 
temperature elevation than that shown by resistance measurement, the ther- 
mometer indication should be accepted. In using the thermometer, care 
should be taken so to protect its bulb as to prevent radiation from it, and, at 
the same time, not to interfere seriously with the normal radiation from the 
part to which it is applied. 

31. In the case of apparatus intended for intermittent service, the tem- 
perature elevation which is attained at the end of the period corresponding 
to the term of full load should not exceed -50° C., by resistance in electric cir- 
cuits. In the case of transformers intended for intermittent service, or not 
operating continuously at full load, but continuously in circuit, as in the ordi- 
nary case of lighting transformers, the temperature elevation above the sur- 
rounding air-temperature should not exceed 50°C. by resistance in electric 
circuits, and 40° C. by thermometer in other parts, after the period correspond- 
ing to the term of full load. In this instance, the test load should not be 
applied until the transformer has been in circuit for a sufficient time to attain 
the temperature elevation due to core loss. With transformers for commercial 
lighting, the duration of the full-load test may be taken as three hours, unless 
otherwise specified. In the case of railway, crane, and elevator motors, the 
conditions of service are necessarily so varied that no specific period cor- 
responding to the full-load term can be stated. 


INSULATION: 


32. The ohmic resistance of the insulation is of secondary importance 
only, as compared with the dielectric strength, or resistance to rupture by 
high voltage. . 

Since the ohmic resistance of the insulation can be very greatly increased 
by baking, but the dielectric strength is liable to be weakened thereby, it is 
preferable to specify a high dielectric strength rather than a high insulation 
resistance. The high-voltage test for dielectric strength should always be 
applied. 

Insulation Resistance. — 

33. Insulation resistance tests should, if possible, be made at the pressure 
for which the apparatus is designed. 

The insulation resistance of the complete apparatus must be such that the 
rated voltage of the apparatus will not send more than t0d5000 of the full-load 


APPENDIX II. 495 


current, at the rated terminal voltage, through the insulation. Where the 
value found in this way exceeds | megohm, 1 megohm is sufficient. 


Dielectric Strength. — 


34. The dielectric strength or resistance to rupture should be determined 
by a continued application of an alternating -£.A7./. for one minute. The 
source of alternating 4.4/./. should be a transformer of such size that the 
charging current of the apparatus as a condenser does not exceed 25 per 
cent of the rated capacity of the transformer. 

35. The high-voltage tests should not be applied when the insulation is 
low, owing to dirt or moisture, and should be applied before the machine is 
put into commercial service. 

36. It should be pointed out that tests at high voltages considerably in 
excess of the normal voltages are admissible on new machines, to determine 
whether they fulfill their specifications, but should not be made subsequently 
at a voltage much exceeding the normal, as the actual insulation of the 
machine may be weakened by such tests. 

37. The test for dielectric strength should be made with the completely 
assembled apparatus and not with its individual parts; and the voltage should 
be applied as follows: — 

Ist. Between electric circuits and surrounding conducting material; and, 

2d. Between adjacent electric circuits, where such exist, as in trans- 
formers. 

The tests should be made. with a sine wave of £./47./,, or where this is 
not available, at a voltage giving the same striking distance between needle 
points in air as a sine wave of the specified 4.4/./., except where expressly 
specified otherwise. As needles, new sewing-needles should be used. It is 
recommended to shunt the apparatus during the test by a spark gap of needle 
points set for a voltage exceeding the required voltage by 10 per cent. 

A table of approximate sparking distances is given in Appendix V. 

38. The following voltages are recommended for apparatus, not including 
transmission lines or switchboards: 


Rated Terminal Voltage. Capacity Testing Voltage. 
Not exceedine 400 volts. 25 ae. a Undenl0- AS = 1000: volts: 


ee ¥ & oe ee OK eh and lovers: 1oUQ) 
400 and over, but less than 800 volts. Under1l0 4%. W. . 1500 «* 
- se bs 1075. Wand over 2000° 


800 “ « 1200 « wee Pa 1 e500". 2% 
1200 ~ Pe OUDT MeV fee etan te rete UOQ » 9% 

2500 De Any § Double the normal 
Z500 i me les Ce -y 


rated voltages. 


Synchronous motor fields and fields of converters started 
fromthe, alternatine current side.) san =. 5000 volts. 

Alternator field circuits should be tested att a Be ndanh test voltage 
corresponding to the rated voltage of the exciter, and referred to an output 
equal to the output of the alternator; i.e., the exciter should be rated for this 
test as having an output equal to that of the machine it excites. 

Condensers should be tested at twice their rated voltage and at their rated 
frequency. 

The values in the table above are effective values, or square roots of 
mean square reduced to a sine wave of £.A7.F. 


496 ELECTRIC LIGHTING. 


39. In testing insulation between different electric circuits, as between 
primary and secondary of transformers, the testing voltage must be chosen 
corresponding to the high-voltage circuit. 

4). In transformers of from 10,000 volts to 20,000 volts, it should be con- 
sidered as sufficient to operate the transformer at twice its rated voltage, by 
connecting first the one, and then the other terminal of the high-voltage wind- 
ing to the core and to the low-voltage winding. The test of dielectric resist 
ance between the low-voltage winding and the core should be in accordance 
with the recommendation in Section 38 for similar voltages and capacities. 

41. When machines or apparatus are to be operated in series, so as to 
employ the sum of their separate /.J/.F.’s, the voltage should be referred 
to this sum, except where the frames of the machine are separately insulated 
both from ground and from each other. 


REGULATION, 


42. The term “regulation” should have the same meaning as the term 
“inherent regulation,” at present frequently used. 

43. The regulation of an apparatus intended for the generation of con- 
stant potential, constant current, constant speed, etc., is to be measured by the 
maximum variation of potential, current, speed, etc., occurring within the range 
from full load to no load, under such constant conditions of operation as give 
the required full-load values, the condition of full load being considered in all 
cases as the normal condition of operation. 

44, The regulation of an apparatus intended for the generation of a poten- 
tial, current, speed, etc., varying in a definite manner between full load and no 
load, is to be measured by the maximum variation of potential current, speed, 
etc., from the satisfied condition, under such constant conditions of operation 
as give the required full-load values. 

If the manner in which the variation in potential, current, speed, etc., 
between full load and no load, is not specified, it should be assumed to be a 
simple linear relation, i.e., undergoing uniform variation between full load and 
no load. 

The regulation of an apparatus may, therefore, differ according to its 
qualification for use. Thus the regulation of a compound-wound generator 
specified as a constant-potential generator will be different from that it 
possesses when specified as an over-compounded generator. 

45. The regulation is given in percentage of the full-load value of potential, 
current, speed, etc.; and the apparatus should be steadily operated during the 
test under the same conditions as at full load. 

46. The regulation of generators is to be determined at constant speed ; of 
alternating apparatus at constant impressed frequency. 

47. The regulation of a generator-unit, consisting of a generator united 
with a prime-mover, should be determined at constant conditions of the 
prime-mover; i.e., constant steam pressure, head, etc. It would include 
the inherent speed variations of the prime-mover. For this reason the 
regulation of a generator-unit is to be distinguished from the regulation of 
either the prime-mover, or of the generator contained in it, when taken 
separately. 

48. In apparatus generating, transforming, or transmitting alternating cur- 


APPENDIX II. 497 


rents, regulation should be understood to refer to non-inductive load ; that is, to 
a load in which the current is in phase with the “.J47./. at the output side of 
the apparatus, except where expressly specified otherwise. 

49, In alternating apparatus receiving electric power, regulation should 
refer to a sine wave of /#.iW./., except where expressly specified otherwise. 

50. In commutating machines, rectifying machines, and synchronous ma- 
chines, as ‘direct-current generators and motors, alternating-current and poly- 
phase generators, the regulation is to be determined under the following 
conditions: 

a. At constant excitation in separately excited fields , 

6. With constant resistance in shunt-field circuits ; and 

.c. With constant resistances hunting series fields; i.e., the field adjust- 
ment should remain constant, and should be so chosen as to give the required 
full-load voltage at full-load current. 

51. In constant potential machines, the regulation is the ratio of the 
maximum difference of terminal voltage from the rated full-load value (occur- 
ring within the range from full load to open circuit) to the full-load terminal 
voltage. 

52. In constant-current machines, the regulation is the ratio of the maxi- 
mum difference of current from the rated full-load value (occurring within the 
range from full load to short circuit) to the full-load current. 

53. In constant-power machines, the regulation is the ratio of maximum 
difference of power from the rated full-load value (occurring within the range 
of operation specified) to the rated power. 

54. In over-compounded machines, the regulation is the ratio of the maxi- 
mum difference in voltage from a straight line connecting the no-load and full- 
load values of terminal voltage as function of the current to the full-load 
terminal voltage. 

55. In constant-speed continuous-current motors, the regulation is the 
ratio of the maximum variation of speed from its full-load value (occurring 
within the range from full load to no load) to the full-load speed. 

56. In transformers, the regulation is the ratio of the rise of secondary 
terminal voltage from full load to no load (at constant primary impressed 
terminal voltage) to the secondary terminal voltage. 

57. In induction motors, the regulation is the ratio of the rise of speed 
from full load to no load (at constant impressed voltage), to the full-load 
‘speed. 

The regulation of an induction motor is, therefore, not identical with the 
slip of the motor, which is the ratio of the drop in speed from synchronism 
to the synchronous speed. 

58. In converters, dynamotors, motor generators, and frequency changers, ~ 
the regulation is the ratio of the maximum difference of terminal voltage at 
the output side from the rated full-load voltage (at constant impressed voltage 
and at constant frequency) to the full-load voltage on the output side. 

59. In transmission lines, feeders, etc., the regulation is the ratio of maxi- 
mum voltage difference at the receiving end, between no-load and full non- 
inductive load, to the full-load voltage at the receiving end, with constant 
voltage impressed upon the sending end. 

60. In steam engines, the regulation is the ratio of the maximum varia- 
tion of speed in passing from full load to no load (at constant steam pressure 
at the throttle) to the full-load speed. 


498 ELECTRICATMIGHIING 


61, In a turbine or other water motor, the regulation is the ratio of the 
maximum variation of speed from full load to no load (at constant head of 
water ; i.e., at constant difference of level between tail race and head race) to 
the full-load speed. 


Variation and Pulsation. — 

62. In prime-movers which do not give an absolutely uniform rate of rota- 
tion or speed, as in steam engines, the “ variation” is the maximum angular 
displacement in position of the revolving member expressed in degrees, from 
the position it would occupy with uniform rotation, and with one revolution 
as 360°; and the pulsation is the ratio of the maximum change of speed in an 
engine cycle to the average speed. 

63. In alternators or alternating-current circuits in general, the variation 
is the maximum difference in phase of the generated wave of 4.4/7.7. from a 
wave of absolutely constant frequency, expressed in degrees, and is due to: 
the variation of the prime-mover. The pulsation is the ratio of the maximum 
change of frequency during an engine cycle to the average frequency. 


64. If 2 = number of poles, the variation of an alternator is s times the 


Te : sete n : i 
variation of its prime-mover if direct-connected, and 3 p times the variation 


of the prime-mover if rigidly connected thereto in the velocity ratio p. 
65. The pulsation of an alternating-current circuit is the same as the pul- 
sation of the prime-mover of its alternator. 


RATING. 


66. Both electrical and mechanical power should be expressed in kilo- 
watts, except when otherwise specified. Alternating-current apparatus should 
be rated in kilowatts on the basis of non-inductive condition; i.e., with the 
current in phase with the terminal voltage. 

67. Thus the electric power generated by an alternating-current apparatus 
equals its rating only at a non-inductive load; that is, when the current is in 
phase with the terminal voltage. 

68. Apparent power should be expressed in kilovolt-amperes as distin- 
guished from real power in kilowatts. 

69, If a power-factor other than 10 per cent is specified, the rating should 
be expressed in kilovolt-amperes and power-factor, at full load. 

70. The full-load current of an electric generator is that current which 
with the rated full-load terminal voltage gives the rated kilowatts, but in alter- 
nating-current apparatus only at non-inductive load. 

71. Thus in machines in which the full-load voltage differs from the no- 
load voltage, the full-load current should refer to the former. 

If P=rating of an electric-generator and / = full-load terminal voltage, 


the full-load current is: 
D) 


Y ss E in a continuous-current machine or single-phase alternator. 


a4 
if ee in a quarter-phase alternator. 
72. Constant-current machines, such as series arc-light generators, should 
be rated in kilowatts based on terminal volts and amperes at full load. 





in a three-phase alternator. 


APPENDIX II. 499 


73. The rating of a fuse or circuit breaker should be the current strength 
at which it will open the circuit, and not the working-current strength. 


Classification of Voltages and Frequencies. — 


74. In direct-current, low-tension generators, the following average termi- 
nal voltages are in general use and are recommended : 
125 volts. 250 volts. 550 volts. 

75. In direct-current, and alternating-current, low-pressure circuits, the 
following average terminal voltages are in general use and are recommended: 
110 volts. 220 volts. 

In direct-current power circuits, for railway and other service, 500 volts 
may be considered as standard. 
76. In alternating-current, high-pressure circuits at the receiving énd, the 
following pressures are in general use, and are recommended : 
1000 volts. 2000 volts. 3000 volts. 6000 volts. 
10000 volts. 15000 volts. 20000 volts. 
77. In alternating-current, high-pressure generators or generating systems 
the following terminal voltages are in general use, and are recommended : 
1150 volts. 2300 volts. 3450 volts. 
These pressures allow of a maximum drop in transmission of 15 per cent 
of the pressure at the receiving end. If the drop required is greater than 15 
per cent, the generator should be considered as special. 
78. In alternating-current circuits, the following approximate frequencies 
are recommended as desirable: 
25 —~ or 30 ~ 40 ~ 60~ 120 ~ (*) 
These frequencies are already in extensive use, and it is deemed advisable 
to adhere to them as closely as possible. 


Overload Capacities. — 


79. All guaranties on heating, regulation, sparking, etc., should apply to 
the rated load, except where expressly specified otherwise, and in alternating- 
current apparatus to the current in phase with the terminal £.A7.F., except 
where a phase displacement is inherent in the apparatus. 

80. All apparatus should be able to carry a reasonable overload without self- 
destruction by heating, sparking, mechanical weakness, etc., and with an increase 
of temperature elevation not exceeding 15° C. above those specified for full 
loads. (See Sections 25 to 81.) 

81. Overload guaranties should refer to normal conditions of operation 
regarding speed, frequency, voltage, etc., and to non-inductive conditions in 
alternating apparatus, except where a phase displacement is inherent in the 
apparatus. 

82. The following overload capacities are recommended : 

1st. In direct-current generators and alternating-current generators: 25 
per cent for one-half hour. 

2d. In direct-current motors and synchronous motors: 25 per cent for 
one-half hour, 50 per cent for one minute; except in railway motors and other 
apparatus intended for intermittent service. 


* The frequency of 120 “ may be considered as covering the already existing commercial fre- 
quencies between 120 ~ and 140 ™, and the frequency of 60 ~ as covering the already existing com- 
mercial frequencies between 60 ~ and ™ 70. 


500 ELECTRICALIGHLIING 


3d. Induction motors: 25 per cent for one-half hour, 50 per cent for one 
minute. 

4th. Synchronous converters: 50 per cent for one-half hour. 

5th. Transformers: 25 per cent for one-half hour; except in trans- 
formers connected to apparatus for which a different overload is guaranteed, 
in which case the same guaranties shall apply for the transformers as for the 
apparatus connected thereto. 

6th. Exciters of alternators and other synchronous machines, 10 per cent 
more overload than is required for the excitation of the synchronous machine 
at its guaranteed overload and for the same period of time. 


APPEN DIAS: 


EP PEC UE IN Gye 


Efficiency of Phase-Displacing Apparatus. — 


In apparatus producing phase displacement, as, for example, synchro- 

nous compensators, exciters of induction generators, reactive coils, condensers, 

olarization cells, etc., the efficiency should be understood to be the ratio of 
the volt-ampere activity to the volt-ampere activity plus power loss. 

The efficiency may be calculated by determining the losses individually, 
adding to them the volt-ampere activity, and then dividing the volt-ampere 
activity by the sum. 

1st. In synchronous compensators and exciters of induction generators, 
the determination of losses is the same as in other synchronous machines 
under Sections 10 and 11. 

2d. In reactive coils the losses are molecular friction, eddy losses, and 
f?r loss. They should be measured by wattmeter. The efficiency of reactive 
coils should be determined with a sine wave of impressed £./47./., except 
where expressly specified otherwise. 

3d. In condensers, the losses are due to dielectric hysteresis and leakage, 
and should be determined by wattmeter with a sine wave of 4.A47.F. 

4th, In polarization cells, the losses are those due to electric resistivity and 
a loss in the electrolyte of the nature of chemical hysteresis, and are usually 
very considerable. They depend upon the frequency, voltage, and tempera- 
ture, and should be determined with a sine wave of impressed £.1/7.F., 
except where expressly specified otherwise. 


AEE NDT ate 
Apparent Efficiency. — 

In apparatus in which a phase displacement is inherent to their operation, 
apparent efficiency should be understood as the ratio of net power output to 
volt-ampere input. 

Such apparatus comprise induction motors, reactive synchronous con- 
verters, synchronous converters controlling the voltage of an alternating-cur- 
rent system, self-exciting synchronous motors, potential regulators, and open 
magnetic circuit transformers, etc. 

Since the apparent efficiency of apparatus generating electric power 
depends upon the power factor of the load, the apparent efficiency, unless 
otherwise specified, should be referred to a load power-factor of unity. 


APPENDIX I. 501 


APRPENDI Xa LIs 
Power Factor and Inductance Factor. — 
The power factor in alternating circuits or apparatus may be defined as 
the ratio of the electric power, in watts, to volt-amperes. 
The inductance factor is to be considered as the ratio of wattless volt- 
amperes to total volt-amperes. 
Thus, if p = power factor, g = inductance factor, 


sige bs Seal 


(energy component of current or £.47.F-.) 
(total current or £.AZ.F. 





The power factor is the 


and the inductance factor is the 
(wattless component of current or &.47./. __ true power. 
(total current or £.4Z.F,, ~ volt amperes. 





Since the power-factor of apparatus supplying electric power depends 
upon the power-factor of the load, the power-factor of the load should be con- 
sidered as unity, unless otherwise specified. 


APPENDIX. LV. 


The following notation is recommended : — 

E, é, voltage, £.47.F., potential difference. . 
/ 7p Current. 

P, power. 

@, magnetic flux. 

®, magnetic density. 

Ae, v7 resistance, 

XG areactance: 

Z, #, impedance. 

ZL, é, inductance. 

Cy cycapacity- 

Vector quantities when used should be denoted by capital italics. 


APE ENDL Xa. 


Table of Sparking Distances in Air between Opposed Sharp Needle- 
Points, for Various Effective Sinusoidal Voltages, in inches and in centi- 
meters. 


DISTANCE. DISTANCE 
KILOVOLTS KILOVOLTS 


SQ. RooT oF SQ. Root or 
MEAN MEAN 
SQUARE. 














KR 
Be Os] 
OU COUN 


0.2 
0.4 
0.7 
1.0 
1.3 
1.6 
2.0 
2.4 
2. 

3. 


O1 60 5 & 

CAAA WORMS 

SONS HS WOOO 

asso 

SEEN S800 Or 
cooos = 

H-RRRACHR ee 


SUSTOH 











AGI LATCO Wt. ne Ge es 
Ageing of Transformer Iron . , 
Alternating Currents . .. . 
Fundamental Waves. . . . 
Harmonic Waves. ... .- 
Cncuits, Caleulationof. a... 
Powercot fieags) es 
Systems of Dewibution® A 6 
Weave, Hormofer = sss cp 
Aluminum asa Conductor . . . 
rAngleiotiar kom, eihcs ts (ols 
Are; the Wlectric<sa,ie. 46 «sss 
[SAP Sr eens) els) en ions 
Arc Lamp, Carbon of Direct Feed 
Cut-outsmeet. a okt ok comes Us 
Composition of the Light . . 


Glatehesipr-utat est ene 
ashe otsue meme ee nee 
Differential Mechanism , . 
Wouble Carbon wea. |.) « 
BOCUSINg 7 me re ae eat tone 
Inverted Sy. aes 


Magnetic Circuits in Mechanisnné 


Mechanisms of Typical Lamps 
Rod Kéed) ©; 
Shunt Mechanism 


Arc Circuits, Incandescent Taube on 


Avculishting  Senes! tame 2 tie 

Brushys yStemien mc eee «tite 
ANCA DANCES: Gb oS & eo 
Arc, the Alternating ..... 


iaclosed fs euccs isms 5 
AD pearaNnCesOL sarees 1s) os 
GarDons:forts- 2, 5 "ees 6 
Candle-Powermol . ©... 
Blowing-out of. . . . 


On Constant Potential ecu : 


Inchosed erases) eee sete 
IEissineofsthe a. enone. 
Efficiency of the 

Resistance of the. «4°. 
Seriessinclosediz. es eons 
Troubles that Occurinthe. . 
Shortees '«-: se sth sue uee. ee 
Wnstableea satu 6 
Watts Consumed by the 


Volts and Amperes Required for ihe 


Belknap Voltage Regulator . . 
BOOSfCES Frome cette me ae oan 
LpaXeretereroh Walia nS Ge 
Method of Feeder Regulation 
Bus bars; Auxiliary so) ose 


ENED exe 


326 to 351 


’ 


303, 312 


5 6) aME 
~ - 99 
. 205 
A 7 
= 5 











Cables for Electric Lighting. . 


(Concenthichemn cats 
Callendémsystemm anys ye ol isiee 
Capacity UE 5 & 


Of Cables ne Canngcrore eS 
Effect on Current eR hie ee 
Hommnulassfon = 0) sien ee ones 
Means of Reducing 
Cardew Earthing Device . 
Circuit-breakers . é 
Chapman Voltage metalation : 
Cleats 


Compound Dosaatee Sais, by 


Composite Wound Alternator . 

Compensator for Voltmeter . 
Motor-Dynamoas- ... . 

Compensated Field Alternator . 


Conductors, Current Capacity and Table ; 


Design and Economyin . . 
Measurementof ..... 
Materials for 

Ovetheadig ea esasee see. |e 
Undersround 9). 28. 9. 4 


Conductivity of Copper . . . 


Coefficient of Change of Resistance . 


Copper,;WireyLable. 29.5) 3. 
Losses in Transformers. . . 
Conductors, Economyin . . 

Constant Potential Regulator . . 
Current Transformer. . . « 


Conduitacastelronea sen ures 
Hibererean ec Verso a cae cite 
Harthen waters. ) ses) een 
(PID CMME raiser 2s) hein a tere 
Wooden... . 5 


Edison Tube Syeterte ae 
Converter, Rotary . 
Cooling of Transformers. . . 
Core Losses in Transformers . . 
(CROSS INTIS Gig ha tone ao 
Crompton Systeme ies lone 
Cut-out, Thomson Film . . 
Cut-out, Cabinet 


PAGE 

BBE rh eeelll 
: . 284 
6 3 200 
6 120 
4 136 
‘ 121 
: 138 
138 

. 176 
. 389 

: 57 
376 

cues 53 
: 193 
199 

5 i EE] 
4g 
13, 15 

10, 87, 226 
é 1 
3 

Are 8 PRI 
262 

4 

‘ 6 
ie 2.5 
SS Hallie: 
10, 87, 226 
mie es ey aH 
76 

a 9 AS 

5 3 2A 

- 269-277 
. 263, 267 
5 PCE IS 
5 Py AG) 
« 696 

: 167 
Ss Peuneloe 
5 247 
: . 279 
regen LAG 
: 392 


Delta Connection, of Three-phase Circuits . 145 


Direct-Current Transformer. . , 
Distribution, Electrical’ 77.) 2) 2 


Alternating Current Systems of . 


From Underground Conduits . 
DG. kranstormenrsmme meus 
Parallel Systems of . . . © 
Polyphase Systems of . . . 
Single-phase Systems of . , 


503 


Sige Fol 
° 4 3 
186 to 223 
a of 6 eal 
ms 93 
enna 28 
eae 200 
5 oo okelh 








504 INDEX. | 
PAGE PAGE 
Distribution, Series Systemsof , . . «5. Ui Inductance- ie) s¢) toes mae connote memes 114 
Dobrowolsky Three-wire System. . .. . @7 Effects, Means of Reducing . .. . . 182 
Donshea Method of Field Excitation . 60 Lay of Corrent due to) 6 .0%% we ede 
Double-Current Generator . .°. .°. . . 215 Table-ob oe Oe nies) ee te 
Drop oes a Te) ay CE Induction Motor. >< % Gal See. so See 
On Mains, Cates ien a Pee era aL tes! Induction, Self and Mutual. . .. . 115 
OmENiets Works a. ie) ese eee eee LOS Insulation . Pri Pe Bria Maree rte Be, Oho’ S09 
Drawing-injof Conductors 27.) 2 eee eos Inferor Conduit ree een tcn cme mae 
Dynamotor 93 Wiring Wee ee 374 
Dynamo, Conpound LBS Iron Losses in Transformers 5 154 
Double 74 
Joints in Cables . 285: 
Economy in Conductors . 10, 87, 226 in Line Wires °° #3 253 
Edison Tube System 1 2id 
Eddy Current Losses . Wee 156 Kelyinis ba. W 2s ese ieas emt enon ere re 
Efficiency of Transformers 159, 161 Kennedyis;System™., .0> 3) 3 2. Se ne ecu: 
All Day, Table . . 163 [Knobmand: Dube Wirlng, 47. . ect t 
Effective Value of A. C. Volts aid eee . 114 
Exciting Current in Transformers , . 125 Lag of Current). - 0. 24. @ se 8s 117 
Lag Due to Inductance 117 
Farad . . 1205 GeadiofiCurrent aes ues 121 
Feeders . Lee ee ee es 884 | Leakage Current in Transformers . 158 
Régulation.) Gaus hoes Y nol 198. | Leakage, Magnetic in Transformers . . . . 150 
Flashing Filaments . 397 | Lightning Arresters . . . . 176 
Filaments of Incandescent laine . 395 , 
Anchored . 407 | Magnetizing Currents in Transformers 158 
Resistance of 410 | Magnetic Leakage in ‘Transformers 150: 
Sizes of . « . 411 Mains, Calculation of . ea 38 
Fished Wiring . 381 Mainsiand apse. | iene) ieee neee ian: . 385 
Five-wire Systems 86 Manholes . « 286 
Fixtures for Lamps . c : 392 Matthiessen’s Standard oA Conductivity A ese Oe 
Flux Densities in Transformer Cc ores 157 Mershon Compensator . . he 199 
Frequency Changer . 218 Mesh Connection. See Delta. 
Frequency . 111 Metersigemecpae site 760) ire el ae ae emcnaie 432-451 
Choice of . : 224 Motor-Converter 93. 
Foucault Current Losses . ; 156 Motor-Dynamo . cae 93 
Fuse Blocks for Transformers . . . . . - 179 Motor-Dynamos as Boosters 99 
ASuGOMpPensatOrs we Eee men 99 
Grounded Shield for Transformers 177 Motor,’tnduction ..% 4. '. ew lan 
Grounding the neutral of 3-wire system Synchronous 147 
84 and App. T Transformer . 93 
of Transformers 177 and App. I Municipal Lighting Grants! Sotelo 
Guard Wires and Hooks . 249 Mutual Induction 115, 134 
Guying Pole Lines . - 246 Inductance of Cireuits : . 131 
Harmonics 1mA- C. Waves i Waked Conductor Underground Systems . 279 
Fenty ; a Networks of Conductors . . 103 
High Voltage D. 3 ‘Distribution . a Current and Drop in . . 103 
Holophane Globe es Desighoe a, pa 
Hysteresis Loss in Transformers ; me Neutral Conductor, Gaoindine ASS 84 and App. I 
TImpedancer as bate 131 
of Parallel Circuits : 126 Over-Compound dynamos, regulation by 53. 
Due to Resistance and iddttanes : 116 Overhead Conductors. . + + + * . 237 
of Series Circuits 126 Insulators for . 248 
Incandescent Lamps 395 Materials for . .. + : ot 
Incandescent Lamp Bases and Beene : 403 PolesiOnecu).) e-Mas wes eeeeromeel ure . a 
Globes 399 SeieeeiNoliodacee Mg of i OF ty C ose 
on Arc Circuits 24 Specifications for. « 4 % 2): )*.% * 237 
Light Distribution 407 er 
Target Diagram : oot ay eee eae Danel Board as ©.” topes see ceine iaatee 
Voltage, Candle- Power Efficiency anda Parallel Systems of Distribution . . . 28 
Life 413 Regulation Gf 24: tows: Gu sue = teen 


INDEX. 505 
PAGE PAGE 
Period and Periodicity, Alternating Current . 111 Switches, Multi-Control. . . Cee OU L 
Pipe’ Conduits: o apes teak ae ees es ee OG Synchronous Polyphase Motors . . .. . 147 
Pole Lines . rer 243-257 
Polyphase Carrents\)?s 1. oa . 141 | Tapering Conductors .. . - es SL 
RMAtora eet eel Leen te ok. ag Target Diagram for Incandesceut eye cere 
Systems of Transmission . . . . . . 200 Temperature Coefficient of Copper . ... 6 
Regulation of) va. uct pate ae 204 WDlaveSS jor WINING Go 6 in go 6 65 & AE 
Transtormers) oo mee ETSA Whree-phases Currents ieee om outs nce La 
Potential Regulator, Indbetion Type gol Fon LOE Three-wire and Five-wire Systems 10-92 
Transtormiers* <. wee poy | SIRS Three-wire System, Auxiliary Generator . . 78 
Power Factors... ee 1 90) Bridgvetarrangvement of (ae) ys en (4: 
Power, Real] and eee of Ny C. Aad naw) with Three-brush Dynamo .... . 76 
Preservation*of Timber. 2. se 244 of A.C. distribution. . . . . . . . 191 
Projectionglcanter nie cimtedins sen fee eed kei on SOD Transfer Bus bars . . - . . «1 + + + 65 
Properties of Conductors . . Ae Rist, OMe Transformers: . 44% 3 + “2 « es, 5 149 
Protective Devices for ‘Transformers ee eel T4 Agemg of Iron in. «4 ee + 5» 150 
ie Deivyebniclency Oty amma ied sere nen tl Oo 
Reactanve; EoOMeF el ays... ee tod Gonstantieurm crite sic umm leon one onl 
@onstructionroleuieunnmes ince meme LOO 


IDuetOLGapaciivar-ma sm. a Ml san sane eran 20) 


Wuestominductanceyes ss.) ie eee ene cO 
Rectifiers baat ase hn ei wast Wee ete ee eed 
Regulation in Constant Potential, A. C. 

SVStCMS Mn mee oulh Ge rete eek 

Parallelusystems "2 vn. .) cue chen en enrol 

Polyphasersystems =) mites eet cue eevee et 

Rotary Dranstormersie reece eee eee OD 

Series! S VStemIS) aetna te ce Sam 

Aber: 5 pea a oe A 6) bes} 
Regulator, Automatic Voltage. . . .. . 57 
Resistance . . . a | opmitatare ho 


Method of pede, Reruiacan bees. ver .03 
Standardi@iasiiy 5. casusm ebro) eh terial isis 


Resonance . . pm oet fo aPlZS 
Return-loop System ‘of Distribubon eo ee OO 
Ran oe Mains aes ee Cee Rey = abe tst oo 
Rotary Converters: favee soa ole Reel oe tO 
Rotary Field! \ au. © see ssn ay LAD 


Rotary Transformers and Revulaion of 
ROO Mya oui se diy, 5, mame kode ee reaarevie. cy LSU, 


Safety Device for Transformers ... . 378 
Sag and Stress in Overhead Wires . . . . 241 
Search) Lamps) 0 J : ile (hte oe OOD. 
Self Inductance, Minar és Reding Ag) geley 
Otjlnesyand Gircultsuens wou, aes Palo 
Series Incandescent Lamps . 24, 25, 422 
Series-Parallel Incandescent Systems . . . 26 
Semmes oystem sArG Lishtnow em. wee ce se od 
Danger from . . Se aE ae, OU 
Distribution of Potential ODM aaa. alo 
Regulation Of 75% cablsbese 6 wene wt sag, FOL 
AltematmeosCurrentm game amet y tem eones) eG 
Ol DISEEIDU TON Nan ie aet aemure ined omer crs ALS 
Service Connections or Loops. . .. . . 255 
Seven-wire Systems .. sts 
Single-phase Parallel "en tovner Sens eo 
Skin ect 5 acon eae cio ctw Seal el oO 
Slips sae ys) ee emew a ie beak cc eer ALS. 
Sockets ees ht ele em ars, 6 OOD 
Split -Insulationysc.ursn: so eee eee saa eee 
StoravesBatteriesgs swyse <!tmasem ie see 


Switches i) 2 <A cn wee leek coo 








CGoolingrot mar. oc. mcn stke ne aes: ay LO 
@oppersWossessau <meta ee ae LS 
(Ones Paes. act nel, My hae eewrtae ene LOM 
IOTICNEMOHE GS Ad el eG ake eg UD 
Hedgehog .. . cite cig i Rote aa OS 
Maecnetic Deakage ime 0. its Se OO lal 


@©pen-circnit- Current ms.) eee LOS 
Roly phase mamice fone ee), enn ers 
Potential skewer ern tater rm ie eet stem eR So 
Protective! Devicesor je urea ene 


Regulationin . . Petrie eau eae te thes’ 
Step-up and Step- dowh ee, Ae mee Loo, 


MReEStin circ Nek caer fuctssk ate cul eeteee BL SO 
Natta ble-ratlore, ai eia ike. iatel rae meme LOO: 
Sizerande ly OCA O less tna imcen irs meme 
Two-phase Currents . . bee ce OO og ee 


Two- and Three-phase Motors: cag ue? Lee ald 


Undersround Conductorss a aes ones nce 


Gables: fOr ss var mee cme, Stace ue sell 
Drawingin . . . A ae are Se aets: 
Earthenware Gonatir i PAN se G8 Aa 
Edisonslube Systemyol ¥ 3 92 20 2 eto 
WINGO RENTS) DOE MGeee art ch git iy me eats 
Manholesfor .. . ote iss ees 200 
Methods of Distribuition eee caries aren 20.1 
Wooden Gonduitstiore. .). aa venue 2h 
Vacuumin Incandescent Lamps : .. 401 
Virtual Values of A. C. Voltage and Current 114 
Violtace-sicimitations al) gm. cnt aimee eeZOO) 


Wiaictle SSACU LECT Carer maaan niece ee 
Wave, Form of A. C. Sas kes ee eae, 
Waves, Fundamental me Homage Bey A iy HeBY 
Weight of Copper for Different Systems . . 226 
Weight of Mains, Calculation of . . . . . 38 
Whre mlnsulatecoa: ven teiisin eMuatgnctacte amircte  s 720 a 


Wiuretlable m=, Mebeenl times rsut seb cetey arc Mrs fey tens 
WiiresuinneslaSteneey aaa cmnen eectmsEn. nem OCS 
Wooden Moulding. 2. <9. 2» « . . . 36 
WidodensOlGSim ce inimici Wants ach beven ole ten no: 20 


‘*Y?? Connection of Three-phase Circuits 145 





‘ x4 : r a SA se ‘/ ty a bs e ry 4 ¢ 
; : ¥ ut 7 Zz 7% 4 ‘ : i. 












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4 VAN NOSTRAND’S LIST OF WORKS 


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ON ELECTRICAL SCIENCE. 5 


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POPE, F. L. Modern Practice of the Electric Telegraph. A Handbook for Elec- 
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6 VAN NOSTRAND’'S LISP: OF WORKS 


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Mlustrated. $1.50. — 


ON ELECTRICAL SCIENCE. 7 


URQUHART, J. W. Dynamo Construction. A Practical Handbook for the use 
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Electric Ship-Lighting. A Handbook on the Practical Fitting and Running of 
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WEBB, H. L. A Practical Guide to the Testing of Insulated Wires and Cables. 
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